HANDICRAFT   SF  PI  FS. 


Cranl 
tion  G, 


UNIVERSITY  OF  CALIFORNIA 

AT   LOS  ANGELES 


THE  GIFT  OF 

MAY  TREAT  MORRISON 

IN  MEMORY  OF 

ALEXANDER  F  MORRISON 


DAVID  McKAY,  Publisher,  1022  Market  Street,  Philadelphia. 


HANDICRAFT  SERIES   (continued}. 

Glass  Working  by  Heat   and   Abrasion.     With  300  Engravings 

and  Diagrams. 

Contents. — Appliances  used  in  Glass  Blowing.  Manipulating  Glass  Tubing. 
Blowing  Bulbs  and  Flasks.  Jointing  Tubes  to  Bulbs  forming  Thistle  Funnels, 
etc.  Blowing  and  Etching  Glass  Fancy  Articles  ;  Embossing  and  Gilding  Flat 
Surfaces.  Utilising  Broken  Glass  Apparatus  ;  Boring  Holes  in,  and  Riveting 
Glass.  Hand-working  of  Telescope  Specula.  Turning,  Chipping,  and  Grinding 
G  ass.  The  Manufacture  of  Glass. 
Building  Model  Boats.  With  168  Engravings  and  Diagrams. 

Contents.- Building   Model    Yachts.      Rigging  and  Sailing  Model  Yachts. 
Making  and  Fitting  Simple   Model  Boats.     Building  a  Model  Atlantic   Liner. 
Vertical  Engine  for  a  Model   Launch.     Model  Launch  Engine  with  Reversing 
Gear.     Making  a  Show  Case  for  a  Model  Boat. 
Electric   Bells,   How  to   Make  and   Fit  Them.    With  162  En- 

graving  s  and  Diagrams. 

Contents. — The  Electr  c  Current  and  the  Laws  that  Govern  it.  Current 
Conductors  used  in  Electric-Bell  Work.  Wiring  for  Electric  Bells.  Elaborated 
Systems  of  Wiring  ;  Burglar  Alarms.  Batteries  for  Electric  Bells.  The  Con- 
struction of  Electric  Bells,  Pushes,  and  Switches.  Indicators  for  Electric-Bell 
Systems. 
Bamboo  Work.  With  177  Engravings  and  Diagrams. 

Contents.— Bamboo  :  Its  Sources  and  Uses.  How  to  Work  Bamboo.  Bamboo 
Tables.  Bamboo  Chairs  and  Seats.  Bamboo  Bedroom  Furniture.  Bamboo 
Hall  Racks  and  Stands.  Bamboo  Music  Racks.  Bamboo  Cabinets  and  Book- 
cases. Bambco  Window  Blinds.  Miscellaneous  Articles  of  Bamboo.  Bamboo 
Mail  Cart. 
Taxidermy.  With  108  Engravings  and  Diagrams. 

Contents.— Skinning  Birds.  Stuffing  and  Mounting  Birds.  Skinning  and 
Stuffing  Mammals.  Mounting  Animals'  Horned  Heads  :  Polishing  and  Mount- 
ing Horns.  Skinning,  Stuffing,  and  Casting  Kish.  P.  eserving,  Cleaning,  and 
Dyeing  Skins.  Preserving  Insects,  and  Birds'  Eggs.  Cases  for  Mounting 
Specimens. 
Tailoring;.  With  180  Engravings  and  Diagrams. 

Contents.—  Tailors'  Requisites  and  Methods  of  Stitching.     Simple  Repairs 
and    Pressing.      Relining,   Repocketing,  and  Recollaring.       How  to  Cut  and 
Make  Trousers.     How  to  Cut  and  Make  Vests.      Cutting  and  Making  Lounge 
and  Reefer  Jackets.     Cutting  and  Making  Morning  and  Frock  Coats. 
Photographic  Cameras  and  Accessories.    Comprising  How  TO 
MAKE  CAMERAS,  DARK  SLICES,  SHUTTERS,  and  STANDS.    With  160 
Illustrations. 

Contents. — Photographic  Lenses  and  How  to  Test  them.   Modern  Half-plate 
Cameras.       Hand   and   Pocket   Cameras.      Ferrotype   Cameras.      Stereoscopic 
Cameras.     Enlarging  Cameras.     Dark  Slides.     Cinematograph  Management. 
Optical  Lanterns.    Comprising  THE  CONSTRUCTION  AND  MANAGEMENT 
OF  OPTICAL  LANTERNS    AND    THE    MAKING  OF  SLIDES.      With    160 
Illustrations. 

Contents.—  Single  Lanterns.  Dissolving  View  lanterns.  Illuminant  for 
Optical  Lanterns.  Optical  Lantern  Accessories.  Conducting  a  Limelight 
Lantern  Exhibition.  Experiments  with  Optical  Lanterns.  Painting  Lantern 
Slides.  Photographic  Lantern  Slides.  Mechanical  Lantern  Slides.  Cinemato- 
graph Management. 
Engraving  Metals.  With  Numerous  Illustrations. 

Contents.  —  Introduction  and  Terms  used.  Engravers'  Tools  and  their  Uses. 
Elementary  Exercises  in  Engraving.  Engraving  Plate  and  Precious  Metals. 
Engraving  Monograms.  Transfer  Processes  of  Engraving  Metals.  Engraving 
Name  Plates.  Engraving  Coffin  Plates.  Engraving  Steel  Plates.  Chasing 
and  Embossing  Metals.  Etching  Metals. 
Basket  Work.  With  189  Illustrations. 

Contents.—  Tools  and  Materials.  Simple  Baskets.  Grocer's  Square  Baskets. 
Round  Baskets.  Oval  Baskets.  Flat  Fruit  Baskets.  Wicker  Elbow  Chairs. 
Basket  Bottle-casings.  Doctors'  and  Chemists'  Baskets.  Fancy  Basket  Work. 
Sussex  Trug  Basket.  Miscellaneous  Basket  Work.  Index 

DAVID  McKAY,  Publisher,  1022  Market  Street,  Philadelphia. 


HANDICRAFT  SERIES   (continued}. 


Bookbinding.     With  125  Engravings  and  Diagrams. 

Contents. — Bookbinders'  Appliances.  Folding  Printed  Book  Sheets.  Beat- 
ing and  Sewing.  Rounding,  Backing,  and  Cover  Cutting.  Cutting  Book  Edges. 
Covering  Books.  Cloth-bound  Books,  Pamphlets,  etc.  Account  Books, 


Contents. — uookDinders  Appliances,  folding  Printed  Book  sheets.  Beat- 
ing and  Sewing.  Rounding,  Backing,  and  Cover  Cutting.  Cutting  Book  Edges. 
Covering  Books.  Cloth-bound  Books,  Pamphlets,  etc.  Account  Book 
Ledgers,  etc.  Coloring,  Sprinkling,  and  Marbling  Book  Edges.  Marbling 
Book  Papers.  Gilding  Book  Edges.  Sprinkling  and  Tree  Marbling  Book 
Covers.  Lettering,  Gilding,  and  Finishing  Book  Covers.  Index. 

Bent  Iron  Work.  Including  ELEMENTARY  ART  METAL  WORK.  With 
269  Engravings  and  Diagrams. 

Contents.— Tools  and  Materials.  Bending  and  Working  Strip  Iron.  Simple 
Exercises  in  Bent  Iron.  Floral  Ornaments  for  Bent  Iron  Work.  Candlesticks. 
Hall  Lanterns.  Screens,  Grilles,  etc.  Table  Lamps.  Suspended  Lamps  and 
Flower  Bowls.  Photograph  Frames.  Newspaper  Rack.  Floor  Lamps. 
Miscellaneous  Examples.  Index. 
Photography.  With  Numerous  Engravings  and  Diagrams. 

Contents  — Ihe  Camera  and  its  Accessories.  The  Studio  and  the  Dark 
Room.  Plates.  Exposure.  Developing  and  Fixing  Negatives.  Intensifica- 
tion and  Reduction  of  Negatives.  Portraiture  and  Picture  Composition. 
Flash-light  Photography.  Retouching  Negatives.  Processes  of  Printing  from 
Negative*.  Mounting  and  Finishing  Prints.  Copying  and  Enlarging.  Stereo- 
scopic Photography.  Ferrotype  Photography. 

Other  Volumes  in  Preparation. 

TECHNICAL  INSTRUCTION. 

Important  New  Series  of  Practical  Volumes.  Edited  by  PAUL 
N.  HASLUCK.  With  numerous  Illustrations  in  the  Text. 
Each  book  contains  about  1 60  pages,  crown  8vo.  Cloth, 
$I.oo  each,  postpaid. 

Practical  Draughtsmen's  Work.    With 226 illustrations. 

Contents.  .-Drawing  Boards.    Paper  and  Mounting.     Draughtsmen's  Instru- 
ments.    Drawing  Straight  Lines.    Drawing  Circular  Lines.     Elliptical  Curves. 
Projection.     Back  Lining  Drawings.    Scale  Drawings  and  Maps.     Colouring 
Drawings.     Making  a  Drawing.     Index. 
Practical  Gasfitting.    With  120  Illustrations. 

Contents.— How  Coal  Gas  is  Made.  Coal  Gas  from  the  Retort  to  the  Gas 
Holder.  Gas  Supply  from  Gas  Holder  to  Meter.  Laying  the  Gas  Pipe  in  the 
House.  Gas  Meters.  Gas  Burners.  Incandescent  Lights.  Gas  Fittings  in 
Workshops  and  Theatres.  Gas  Fittings  for  Festival  Illuminations.  Gas  Fires 
and  Cooking  Stoves.  Index. 

Practical  Staircase  Joinery.    With  215  illustrations. 

.Contents. — Introduction  :  Explanation  of  Terms.  Simple  Form  of  Staircase 
—Housed  String  Stair  :  Measuring,  Planning,  and  Setting  Out.  Two-flight 
Staircase.  Staircase  with  Winders  at  Bottom.  Staircase  with  Winders  at  Top 
and  Bottom.  Staircase  with  Half-space  of  Winders.  Staircase  over  an  Oblique 
Plan.  Staircase  with  Open  or  Cut  Strings.  Cut  String  Staircase  with  Brackets. 
Open  String  Staircase  with  Bull  nose  Step.  Geometrical  Staircases.  Winding 
Staircases.  Ships'  Staircases.  Index. 

Practical  Metal  Plate  Work.    With 247 Illustrations. 

Contents.— Materials  used  in  Metal  Plate  Work.  Geometrical  Construction 
of  Plane  Figures.  Geometrical  Construction  and  Development  of  Solid 
Figures.  Tools  and  Appliances  used  in  Metal  Plate  Work.  Soldering  and 
Brazing.  Tinning.  Re-tinning  and  Galvanising.  Examples  of  Practical 
Metal  Plate  Work.  Examples  of  Practical  Pattern  Drawing.  Index. 

Practical  Graining  and  Marbling.    With  79  illustrations. 

Contents.— Graining:  Introduction,  Tools,  and  Mechanical  Aids.  Graining 
Grounds  and  Graining  Colors.  Oak  Graining  in  Oil.  Oak  Graining  in  Spirit 
and  Water  Colours.  Pollard  Oak  and  Knotted  Oak  Graining.  Maple  Graining 
Mahogany  and  Pitch-pine  Graining.  Walnut  Graining.  Fancy  Wood  Grain- 
ing. Furniture  Graining.  Imitating  Woods  by  Staining.  Imitating  Inlaid 
Woods.  Marbling:  Introduction,  Tools,  and  Materials.  Imitating  Varieties 
of  Marble.  Index. 

Ready  Shortly:  Practical  Plumbing  Work. 

Other  New  Volumes  in  Preparation. 
DAVID  McKAY,  Publisher,  1022  Market  Street,  Philadelphia. 


"  WORK"    HANDBOOKS. 


DYNAMOS  AND  ELECTRIC  MOTORS 


THE 
A.F. 
MEMORIAL  LIBRARY 


DYNAMOS  AND  ELECTRIC 
MOTORS 

HOW  TO  MAKE  AND  RUN  THEM 

WITH  NUMEROUS  ENGRAVINGS  AND  DIAGRAMS 


EDITED    BY 

PAUL  N.  HASLUCK 
»» 

EDITOR    OF     "WORK"    AND    "BUILDING    WORLD," 
AUTHOR    OF    "  HAKDYBOOKS    FOR    HANDICRAFTS,"    ETC.    ETC. 


PHILADELPHIA 

DAVID    McKAY,   PUBLISHER 

1022,    MARKET  SJREET 
1903 


PREFACE. 

THIS  Handbook  contains,   in   a   form   convenient   for 
everyday  use,  a  comprehensive  digest  of  the  informa- 
tion on  How  to  Make  and  Run  Small  Dynamos  and 
Electric  Motors,  scattered  over  ten  thousand  columns 
««    of  WORK,  one  of  the  weekly  journals  it  is  my  fortune  to 
K    edit— and  supplies  concise  information  on  the  general 
g=     principles  of  the  subjects  on  which  it  treats. 

In  preparing  for  publication  in  book  form  the  mass 
of  relevant  matter  contained  in  the  volumes  of  WORK, 
C  much  that  was  tautological  in  character  had  to  be  re- 
g  jected.  The  remainder  necessarily  had  to  be  arranged 
£  anew,  altered  and  largely  re-written.  From  these 
Z  causes  the  contributions  of  many  are  so  blended  that 
the  writings  of  individuals  cannot  be  distinguished  for 
acknowledgment. 

Readers  who  may  desire  additional  information  re- 
specting special  details  of  the  matters  dealt  with  in 
this  Handbook,  or  instruction  on  kindred  subjects, 
should  address  a  question  to  WORK,  so  that  it  may 
be  answered  in  the  columns  of  that  journal. 

P.    N.    HASLUCK. 

I.'t  Belle  Saw>.ioe,  London. 


434360 


CONTENTS. 

CHAP.  PAGfi 

I. — Introduction         ......        9 

II. — The  Siemens  Dynamo         .        .        .        .21 

III.— The  Gramme  Dynamo        .        .        .        .41 

IV.— The  Manchester  Dynamo    ....      61 

V.— The  Simplex  Dynamo         ....      66 

VI.— Calculating    the    Size    and    Amount    of 

Wire  for  Small  Dynamos      ...      76 
VII. — Ailments       of     Small     Dynamo-Electric 

Machines  :   their  Causes  and  Cures     .      89 
VIII.— Small  Electric  Motors  without  Castings     .      98 
IX. — How     to    Determine    the    Direction    of 

Rotation  of  a  Motor     .        .        .        .112 

X.— How  to  Make  a  Shuttle- Armature  Motor    119 
XI.— Fifty- Watt  Undertype  Dynamo         .        .129 
XII.— Four-Hundred-and-Forty  Watt  Manchester 

Type  Dynamo         .  ,  144 


LIST    OF    ILLUSTRATIONS. 


ria.                                             PA 

1.—  Undertype  Field  Maguet 
2.—  Overtype  Field  Magnet  . 

i-i 

via.                                            PAGE 
36.—  Commutator       Bearing, 
showing    Position     of 

3.-Single  Coil  Field  Magnet 

n 

Brushes. 

M 

4,-Manchester  Field   Mag- 

37.— Brush  Clamp    . 

80 

net  

];> 

38-40.—  Forms  of  Brushes 

::i 

5.—  Gramme  Field  Magnet   . 

l.'I 

41.—  Position  of  Brushes  for 

6.—  Plain  Ring  Armature      . 
7.—  Cogged  Ring  Armature  . 

15 

is 

Shuttle  Armature 
42.—  Siemens   Type    Dynamo 

n 

8.—  H-girder  Armature. 

u 

complete 

36 

9.—  Double  Shuttle  Armature 

is 

43.—  Magnetising  Field  Mag- 

10.— LaminatedShuttle  Arma- 

nets      .... 

37 

ture  :  Side  Elevation    . 

16 

44.—  Diagram  of  Series  Con- 

11.— Centre    Stampings     for 

nections         .       .       . 

39 

Laminated  Armature  . 

17 

45.—  Diagram  of  Shunt  Con- 

12.— End        Stampings       for 

nections.                . 

M 

Laminated  Armature  . 

17 

46.  —  Gramme    Dynamo  com- 

IS.—  End    View    of     Shuttle 

pleto       .... 

41 

Armature 

17 

47.  —  Iron  Carcase  of  Gramme 

14.—  Straight  Pattern  Binding- 

Dynamo. 

42 

Post       .... 

is 

48.—  Inner  Face  of  Standard 

15.—  Ball    Pattern     Binding- 

with  Bridge  for  Brush- 

Post        .... 

is 

Holders  . 

43 

16,  17.—  Telegraph       Pattern 

49.—  Magnet       Cores       with 

Binding-Posts 

19 

Flanges. 

44 

18.—  Flat  Base  Terminal  . 

19 

50.—  Laminated  Iron   Punch- 

19.—  Wing  Nut  Terminal 
20.—  Nut  and  Piu  Terminal     . 

20 

211 

ing  for  Armature  . 
51.  —  Spider     for     Laminated 

45 

21.—  Wire  Connector       . 

20 

Armature 

46 

22.  —  Outline       of       Siemens 

52.  —  Portion  of  Ring  Armature 

Dyuauio  .... 

21 

ready  for  Winding 

47 

23,  24.-Forms  of  Field  Mag- 

53.—  Armature      Spindle     of 

nets     for     Undertyt-e 

Gramme  Armature 

48 

Dynamos 

22 

54.  —  Commutator     for    Ring 

25.-Solid  H-girder  Armature, 

Armature  complete     . 

49 

CommeuciUf;  to  Wind  . 

23 

55.—  How    to     divide     Com- 

26.— Spimllo     Holder  :      End 

mutator  Ring        .       . 

49 

View       .... 

2-, 

5f>.—  How   to   insulate   Com- 

27. -Section  of  Spindle  Holder 
2S.^Sectiou  of  Spindle  Holder 
and  Commutator  . 

25 
19 

mutator  Segments 
57.—  Copper    Connector     for 
Ends  of  Armature  Coils 

49 
51 

29.—  Laminated  Iron  Punch- 

58.-Woo"den     Shuttle      for 

ing  for  Armature  . 

M 

winding  Armatures 

52 

30.  —  Iron  Laminations  Strung 

59.—  Connection  of  Armature 

on  Spindle     ,       . 

M 

Coils  to  Commutator  . 

M 

31.—  Bearings  for  Armature  : 

60.-Rockerfor  Brush-Holder 

U 

End  View      . 

n 

61  —  Brush-Holderaud  Rocker 

32.  —  Bearings  for  Armature  : 

complete 

56 

Section  .... 

u 

62.—  Clamp  for  Brushes  . 

56 

33.—  Brass     Ring     for    Com- 

63.— Winding  Field  Magnets 

mutator.        .        . 

29 

of  Gramme  Dynamo    . 

57 

34.—  Split-tube  Commutator  . 

n 

64.—  Connecting     Fields     in 

35.—  Section      of      Complete 

Series  and  in  Shunt 

58 

Armature 

30 

65.  —  Manchester  Dyuaino 

til 

LIST  OF  ILLUSTRATIONS. 


HO.  PAGE 

66.— Section  of  Manchester 
Dynamo.showing  wind- 
ing of  Field  Magnet 
Cores  .  .  .  62 

91.— Magnet  Core  for    Man- 
chester Dynamo   .        .      63 
68.— Magnet  Core  with  Fillets 

to  receive  Flanges  .  63 
69.— Magnet  Core  fitted  with 

Iron  Flanges          .        .      63 
70.— Former  for  making  Sim- 
plex Armature  Core     .      67 
71. — Clamp  for  Armature  Core      68 
72.— Method  of  winding  Ring 

Armature      ...      68 
73. — Wooden  Plug  for  Arma- 
ture       ....      69 
74.— Commutator  of  Simplex 

Dynamo  ...  70 
75. — Armature  of  Simplex 

Dynamo  complete  .  71 
76.-Pul«  Piece  of  ditto  .  .  72 
77.— Yoke  for  Magnet  of  ditto  72 
78.— Coil  Flange  ...  72 
79.— Bed-Plate  of  Simplex 

Dynamo  ...  73 
80. — Bearings  of  Armature  .  73 
81.— Brush-Holder  ...  74 
82. — Simplex  Dynamo  com- 
plete ....  74 
83.— Section  of  Shuttle 

Armature  ...  85 
84.— Side  View  of  ditto  .  .  85 
85.— Section  of  Cog  -  ring 

Armature  ...  86 
86.— Side  View  of  ditto  .  .  87 
87.— Simple  Electric  Motor 

complete  I  .  .  .98 
88.— Side  Elevation  of  Field 

Magnet  and  Block  .  99 
89.— Plan  of  Field  Magnet 

and  Block  ...  100 
90.— Front  Elevation  of  ditto.  101 
91.— Armature,  showing  f-in. 

Limit      ....     102 
92.— Shape  of  Brush         .        .     102 
93.— Face  of  Commutator       .    102 
94. — Armature  Shaft  complete    103 
95.— End  View  of  Brass  Bear- 
ing for  Armature  Shaft     104 
96.— End  View  of  Miniature 
Electric    Motor     with 
Iron  Yoke      ...    106 
97._Side  Elevation  of  ditto    .    106 
98.— Side  Elevation  of  Small 
Motor  with  Horse-shoe 
Magnet    and   Wooden 
Saddle    ....    107, 
99.— End  Elevation  of  ditto    .    107 
VOO.— Plan  of  ditto     .  108 


FIO.  PAflE 

101.— Bearing  Brackets  .  .  108 
102.— Bobbin  for  Magnet  Coils  109 
103.—  Horse-shoe  Magnet.  .  110 
104.— Iron  Armature .  .  .  110 
105.— Setting  -  out  Contact 

Breaker.  .  .  .110 
106.— Fly  -  wheel  Armature 

and  Contact  Breaker    .     110 
107-110.— Directions    of     Cur- 
rents   and     Resultant 
Magnetism       in       Bar 
Magnets         .        .        .113 
111,  112.— Series  Motors   .        .114 
113,  114.— Shunt  Motors  .        .     116 
115,  116. — Motors  driven    with 

Two  Batteries  .  .  117 
117.— Shuttle- Armature  Motor 

complete        .        .        .119 
118.— Field     Magnet     Casting 
for  Shuttle  -  Armature 
Motor     ....    120 
119.— Armature     Casting     for 
Shuttle-Armature  Mo- 
tor  121 

120.— Gun-metal    Casting    for 

Armature  Ends  .  .  121 
121.— Gun  -  metal  Foot  for 

Motor  .  .  .  .122 
122.— Rocker  for  Brush  - 

Holders.  .  .  .122 
123.— Castingfor  Brush-Holder  123 
124.-Casting  for  Milled  Head 

Screw  ....  123 
125.— Brush-Holder  complete.  124 
126.— Brass  Screw  with  Milled 

Head  ....  124 
127.— Brush  .  .  .  .124 
128.— Commutator  ...  125 
129.— Section  of  Motor,  show- 
ing winding  ...  129 
130,-Brush -Holders,  Rocker, 

and  Brushes  complete  128 
131.— Plan  of  Dynamo  .  .  132 
132.— Side  View  of  ditto  and 

Motor  ....  133 
133.— End  View  of  ditto  .  .  136 
13K— Side  View  of  Armature  .  138 
135.-End  View  of  Armature  .  138 
136.— Field  Magnets  showing 

Method  of  Winding  .  141 
137. — Position  of  Commutator.  142 
138.— Plan  of  Manchester  Dy- 
namo .  .  .  .  14i 
139.— End  View  of  ditto  .  .  147 
140.— Longitudinal  Section  of 

ditto        .        .        .        .148 
141.— End  View,  showing  me- 
thod of  winding  Arm- 
ature and  Fields  .        .    151 
142.— Brush  Gear       .  .    152 


DYNAMOS  &  ELECTRIC 
MOTORS. 


CHAPTER   I. 

INTRODUCTION. 

SINCE  the  invention  of  the  first  dynamo  in  1832,  by 
Pixii,  the  machine  has  passed  through  many  phases  of 
evolution.  It  began  under  the  name  of  a  magneto- 
electric  machine,  and  continued  to  bear  this  name  whilst 
permanent  steel  magnets  were  employed  in  its  con- 
struction. It  was  then  as  truly  a  dynamo  as  any  one 
of  its  successors,  because  the  permanent  magnets  only 
acted  as  required  when  moved.  It  is  not  intended  in 
this  Handbook  to  give  a  history  of  the  machine,  but 
to  show  how  to  make  small  examples  of  those  which  are 
now  in  general  use  for  electric  lighting  purposes.  These 
may  be  arranged  in  classes  named  according  to  the 
types  of  armatures,  or  of  the  field  magnets  used  in 
their  construction. 

Before  describing  either  the  dynamo  or  its  action,  it 
would  be  as  well  to  consider  when  and  why  the  dynamo- 
electric  machine  is  used,  instead  of  primary  batteries,  as 
a  means  of  generating  electricity  for  lighting  lamps,  etc. 
In  the  first  place,  the  lighting  of  electric  lamps  by  the 
agency  of  primary  batteries  is  only  practicable  under 
somewhat  restricted  conditions.  To  get  a  sufficiently 
high  electro  motive  force  it  is  necessary  to  have  a 
great  number  of  cells  connected  in  series,  and  big  cells 
are  required  to  provide  the  current,  or  the  battery  will 
soon  run  down.  When  a  cell  is  required  to  give  a  current 
of  three  amperes  or  more,  it  polarises  very  rapidly ; 
hence  to  lower  the  resistance  of  the  lamp  circuit  (as  by 


io  DYNAMOS  AND  ELECTRIC  MOTORS. 

placing  the  lamps  in.  parallel)  4s  costly  and  inconvenient, 
as  a  greater -demand  ^fbr  current  is  thus  thrown  on  the 
battery.  .  Then  the  costly,  .dirty,  and  laborious  job  of 
cleaning  ]  and  tGcliarglhg  the  Tells-  is  enough  to  make 
one  wish  for  some  better  method  of  generating  the 
electric  current. 

Small  electric  lights,  such  as  night-lights  and  occa- 
sional lights  of  low  candle  power,  may  be  fed  with  a  small 
two-cell  chromic  acid  battery,  or  even  a  Fuller  bichromate 
battery.  But  when  the  area  of  lighting  is  extended,  a 
dynamo-electric  machine  is  generally  used.  This  is  a 
machine  for  converting  mechanical  energy  into  electric 
energy. 

There  are  many  who  believe  that  electricity  actually 
runs,  or  flows,  from  one  end  of  a  wire  or  conductor  to 
the  other,  in  a  certain  direction,  when  the  ends  are 
connected  to  a  battery  or  dynamo.  For  instance,  in 
the  case  of  a  battery  of  primary  cells,  the  current  is 
always  spoken  of  as  coming  from  the  carbon  terminal, 
going  through  the  external  circuit,  and  returning  to  the 
zinc.  This,  in  point  of  fact,  is  misleading  ;  for  the  expres- 
sion is  quite  conventional,  and  it  might  easily  have  been 
expressed  the  other  way,  and  would  have  made  no 
difference  whatever  to  electrical  formulae  or  laws.  But 
when  electricity  came  to  be  studied  and  advance  was 
made  in  the  science,  it  was  mutually  agreed  to  express 
the  phenomenon  in  this  way. 

In  a  similar  manner  it  was  agreed  to  call  one  end  of 
a  magnet  the  north  pole,  and  the  other  the  south  ;  but 
in  this  case  we  are  brought  face  to  face  with  a  paradox. 
It  is  this :  either  we  have  all  along  been  giving  our 
magnet  ends  wrong  names,  or  else  Franklin,  and  many 
others  after  him,  have  diligently  been  searching  the 
Arctic  Seas  for  the  North  Pole  when  it  is  the  south 
all  the  time  ;  for  like  poles  repel  each  other,  unlike 
poles  attract  Perhaps  it  has  been  noticed  that  many 
writers  are  careful  in  calling  the  two  ends  of  a  magnet 
the  north-seeking  and  south-seeking  poles  respectively. 

But  as  regards  an  electric  current,  this  conventional 


INTRODUCTION.  1 1 

way  of  expressing  it  must  not  be  taken  literally. 
Electricity  is  not  a  liquid  ;  it  does  not  flow  through 
a  certain  wire  as  water  through  a  pipe.  Although 
water  is  a  very  useful  substance  to  make  use  of  as  an 
example  when  studying  some  of  the  phenomena  of 
electricity,  yet  electricity  is  unlike  water  in  many  ways 
— it  can  be  said  to  work  uphill;  it  is  not  influenced 
by  the  force  of  gravity ;  also,  it  can  be  said  to  act 
two  ways  at  once. 

Whatever  electricity  may  be,  it  is  perfectly  clear  at 
the  present  time  that  sources  of  electrical  energy  have 
different  effects  upon  different  substances,  copper,  silver, 
and  other  metals  being  very  susceptible  to  this  influence. 
Hence,  these  metals  are  called  the  best  conductors. 
But  glass,  vulcanite,  paraffin  wax,  and  most  com- 
pound substances  are  considered,  in  one  sense,  bad 
conductors— some  say  non-conductors. 

The  actual  time  it  takes  a  current  of  electricity  to 
traverse  a  given  length  of  wire  is  often  stated  and 
put  down  to  be  some  fraction  of  a  second  ;  but  it  must 
on  no  account  be  understood  from  this  that  the  current 
flows  from  its  source  in  one  direction  right  round 
the  circuit  and  back  again  to  that  source  ;  but  that 
a  "condition"  is  set  up,  when  the  circuit  is  closed, 
both  ways  along  the  conductor  or  wire. 

As  far  as  we  know,  in  an  electric  circuit  nothing 
can  actually  be  said  to  flow  from  one  end  to  the 
other,  but  it  is  a  "condition"  set  up  throughout  the 
entire  length ;  and  this  length  must  form  a  complete 
circuit  or  ring,  the  shape  of  which  matters  little.  Also, 
somewhere  within  this  circuit,  and  forming  part  of  it, 
must  be  placed  the  means  of  setting  up  this  "condition" 
—say,  a  battery  or  a  dynamo. 

The  following  outlines  represent  the  field  magnets  of 
some  dynamos  in  general  use  : — Undertype,  Fig.  1  : 
Two  vertical  cores  of  rectangular  section  joined  to  the 
pole-pieces,  cast  with  armature  tunnel  in  lower  part 
Similar  machines  have  cores  of  circular  section.  Over- 
type, Fig.  2  :  Two  vertical  cores  of  suitable  section  cast 


DYNAMOS  AND  ELECTRIC  MOTORS. 


with  yoke  at  base,  and  the  armature  tunnel  in  upper 
part.  Coils  may  be  wound  separately,  then  slipped 
over  cores.  Several  modifications  of  this  machine 
have  been  designed.  Some  of  these  have  round  cores. 
Single  coil  or  simplex,  Fig.  3  :  One  core  of  circular 
section  joined  to  suitable  pole-pieces  with  the  armature 
tunnel  at  the  side.  In  one  form  this  machine  has  it? 
single  core  spanning  horizontally  the  two  vertical  pole- 
pieces,  with  the  armature  tunnel  in  the  upper  part 
Manchester,  Fig.  4  :  Two  cores  of  circular  section 
bedded  into  two  horizontal  pole-pieces.  Armature 
tunnel  in  the  central  part  of  the  machine  between  the 


Fig.  1.— Uudertype  Field 
Magnet. 


Fig.  2.— Overtype  Field 
Magnet. 


two  cores.  Gramme ,  Fig.  5  :  Four  horizontal  cores  of 
circular  section  bedding  into  massive  pole-pieces  in  the 
centre  of  the  machine,  and  into  vertical  standards  at 
the  sides  ;  armature  tunnel  in  centre  of  the  machine. 

The  field  magnets  of  these  machines  are  not  made 
up  of  steel  permanently  magnetised,  but  are  constructed 
of  comparatively  soft  iron,  containing  residual  mag- 
netism, which,  by  dynamic  energy  imparted  to  the 
armature,  is  induced  to  exert  its  influence  on  the  arma- 
ture coils,  and  create  in  them  an  electric  current.  This 
current,  or  part  of  it,  is  then  sent  around  the  field 
magnet  coils,  with  the  result  that  a  stronger  magnetism 
is  induced  in  the  cores  of  the  field  magnets.  Being 
thus  strengthened,  they  induce  a  higher  electro-motive 
force  in  the  armature  coils,  and  thus  the  full  electric 
power  of  the  machine  is  worked  up 


INTRODUCTION. 


Now  as  to  the  way  in  which  a  current  of  electricity 
is  measured.  The  unit  of  current  generally  accepted 
is  the  Ampbre.  Some  idea  of  its  meaning  may  be 
learned  by  comparison  with  other  units  of  measure- 
ment. For  instance,  in  trades  where  the  foot  rule  is 
used,  the  foot  and  inch  are  units  of  measurement  of 
length.  Where  steam  engines  are  used,  we  speak  of 


Fig.  ,3.— Single  Coil  or  Sim- 
plex Field  Magnet. 


Fig.  4.— Manchester  Field 
Magnet. 


pounds  per  square  inch  in  estimating  the  pressure  of 
Bteam;  and  horse-power  as  a  unit  in  estimating  the 
power  of  a  steam  engine.  Where  water  is  used  as  a 


Fig.  5. — Gramme  Field  Magnet. 

motive  power,  we  speak  of  its  volume  by  cubic  inches, 
or  gallons.  In  dealing  with  electrical  measurements, 
neither  the  foot  rule  nor  the  spring-pressure  gauge  can 
be  used,  so  electricians  have  had  to  invent  a  new  set 
of  instruments,  and  new  names  for  the  units  or  divisions 
marked  on  them. 

The  Ampere  is  defined  as  that  current  which  is 
obtained  when  an  electro-motive  force  of  one  Volt 
acts  on  a  resistance  of  one  Ohm.  A  volt  is  the  unit 
measure  of  electro-motive  force  roughly  as  given  by  the 


14  DYNAMOS  AND  ELECTRIC  MOTORS. 

current  from  one  standard  Daniell  cell ;  a  better 
standard  is  the  Hibbert  one-volt  cell  recently  intro- 
duced. An  ohm  is  the  unit  of  resistance.  A  10-feet 
length  of  '01  inch  copper  wire  of  95  per  cent,  con- 
ductivity has  roughly  one  ohm  resistance.  If  we 
divide  the  total  electro-motive  force  in  volts  by  the 
total  resistance  of  the  circuit  in  ohms,  we  obtain  the 
value  or  strength  of  the  current  in  amperes.  For 
measuring  amperes,  an  ampere-meter,  or  ammeter,  is 
used,  and  voltmeters  are  used  for  measuring  the  voltage  or 
potential  difference  between  different  points  of  a  circuit. 

The  Watt  is  the  electrical  unit  of  power  or  activity. 
Just  as  the  rate  at  which  an  engine  works  is  measured 
by  horse-power,  so  the  rate  of  output  of  a  dynamo  is 
measured  in  watts.  Therefore  to  measure  the  output 
of  a  dynamo  in  this  way  multiply  the  electro-motive 
force  at  the  terminals  of  the  machine,  in  volts,  by  the 
current  in  the  external  circuit,  in  amperes.  Thus,  watts 
equal  volts  multiplied  by  amperes.  Very  nearly,  1 
horse-power  equals  746  watts. 

An  Ampere  hour  is  a  term  frequently  met  with,  and 
means  one  ampere  supplied  or  required  for  the  space 
of  one  hour,  or  the  equivalent.  Thus  amperes  multi- 
plied by  hours  gives  ampere  hours.  For  instance,  an 
accumulator  that  is  said  to  have  a  capacity  of  eighty 
ampere  hours,  is  one  that  might  give  a  current  of  1 
ampere  for  eighty  hours,  2  "amperes  for  forty  hours,  or 
4  amperes  for  twenty  hours  and  so  on. 

Armature  is  a  name  given  to  the  iron  keeper  of  a 
permanent  magnet.  In  dynamos  it  is  applied  to 
that  part  which  is  rotated  within  the  influence  of 
the  field  magnets.  There  are  some  exceptions,  in 
which  the  magnets  are  caused  to  revolve  arid  the 
armature  is  stationary.  Revolving  armatures  and  fixed 
field  magnets  have  the  merit  of  adding  stability  to  the 
machine  and  steadiness  to  its  running  and  the  output  of 
the  current.  Each  inventor  of  a  new  dynamo  appears 
at  first  to  have  adopted  a  special  form  of  armature; 
henco  we  have  almost  as  many  forms  of  armature  as  there 


I  NT  ROD  UC  TION.  1 5 

are  inventors  of  machines.  The  armatures  are  generally 
furnished  with  iron  cores,  around  which  insulated  copper 
wires  are  wound.  Machines  have  been  constructed  with- 
out iron  cores,  by  Messrs.  Siemens,  Ferranti,  Mordey 
and  Thompson.  In  some  of  those  machines  a  looped 
or  zigzag  band  of  copper  has  been  attached  to  a  brass 


Fig.  6.— Plain  Ring 
Armature. 


Fig.  7.— Cogged  Ring  or 
Pacinotti  Armature. 


spider,  mounted  on  a  spindle,  and  forms  the  arma- 
ture. By  Lord  Kelvin  all  armatures  are  divided  into 
four  types  : — 


Fig.  8.— Shuttle 
or  H-girder  Armature. 


Fig.  9.— Double  Shuttle  or 
Walker  Armature. 


(1)  Ring  armatures,  in  which  the  coils  are  grouped 
upon  a  ring  whose  principal  axis  of  symmetry  is  also 
its  axis  of  rotation. 

(2)  Drum  armatures,  in  which  the  coils  are  wound 
longitudinally  over  the  surface  of  a  drum  or  cylinder. 

(3)  Pole  armatures,  having  coils  wound  on  separate 
poles  projecting  radially  from  a  disc  or  central  hub. 

(4)  Disc  armatures,  in  which  the  coils  are  flattened 
against  a  disc. 


16  DYNAMOS  AND  ELECTRIC  MOTORS. 

Of  these  it  is  as  well  to  say  that  early  examples  of  the 
first  type  were  furnished  by  the  machines  of  Gramme, 
Schuckert,  Giilcher,  and  Brush.  Examples  of  the 
second  type  are  to  be  found  in  the  Siemens  (Alteneck), 
Edison,  Weston,  and  Elphinstone- Vincent  machines. 
Examples  of  the  third  type  were  to  be  seen  in  the 
dynamos  of  Elmore  and  Lontin.  There  are  but 
few  useful  examples  of  the  fourth  type,  except  the 
Desrosier. 

When  solid  iron  is  employed  for  an  armature  core, 
eddy  currents  are  set  up  in  the  iron,  and  cause  the 


~S     j  

m> 
-  1 

t 

Fig.  10.— Laminated  Shuttle  Armature. 

armature  to  become  hot.  Iron  armatures  should  there- 
fore be  built  up  of  thin  sheet-iron  discs,  or  plates  of  hoop 
iron,  each  layer  of  iron  being  magnetically  insulated 
from  its  neighbour  by  varnished  paper  or  calico.  The 
armature  coils  should  be  of  pure  copper  wire,  well 
insulated  with  silk  or  cotton,  and  the  wires  should  be 
as  short  and  thick  as  is  consistent  with  obtaining  the 
requisite  electro-motive  force  without  driving  the 
machine  at  an  excessive  speed. 

Figs.  6  to  9  show  the  types  of  armatures  in  use  for 
small  dynamos  and  electric  motors.  Fig.  6  shows  a  plain 
ring  armature.  It  is  generally  formed  of  rings  or  collars 
of  very  thin  sheet  iron.  These  may  be  strung  together 
on  gun -metal  bolts,  attached  to  the  arms  of  brass  spiders 
as  shown  by  the  dotted  lines,  the  armature  spindle 
going  through  the  hole  in  the  centre.  The  rings  are 
\Tound  with  several  coils  of  wire,  passing  through 


fXTRODUCTIOff, 


and  over  the  rings.  They  can  also  be  wound  as  a 
drum  by  winding  the  coils  over  the  rings  only.  The 
drum  armature  may  also  be  made  of  discs  instead  of 
rings.  Fig.  7  shows  a  cogged  ring  or  Pacinotti  armature. 
This  also  is  made  of  rings  stamped  from  thin  sheet 
iron,  which  may  be  strung  on  bolts  attached  to  brass 
spiders.  Small  armatures  are  sometimes  cast  solid  in 
soft  malleable  iron.  The  cogs  and  spaces  may  vary  from 


Fig.  11.— Centre  Stamp- 
ings  for  Laminated 
Shuttle  Armature, 


Fig.  12.— End  Stampings  for 
Laminated  Shuttle  Arma- 
ture. 


Fig.  13.— End  View  of  Shuttle  Armature. 

six  to  sixteen,  and  the  number  of  coils  is  determined 
by  the  number  of  spaces  between  the  cogs.  Fig.  8 
shows  in  section  a  shuttle  or  H-girder  armature.  In 
small  machines  this  is  cast  solid.  It  is  also  built  up 
of  laminated  stampings  of  sheet  iron  strung  on  a  steel 
spindle.  One  coil  only  can  be  wound  on  a  shuttle 
armature.  Fig.  9  shows  a  double  shuttle  or  Walker 
armature,  also  built  of  sheet  iron  stampings.  A  coil 
may  be  wound  on  each  arm,  making  four  coils  in  all, 
or  two  coils  may  be  wound  crosswise.  It  is  not  a 
good  armature  to  wind,  as  the  coils  are  apt  to  be  of 


i8          DYNAMOS  AND  ELECTRIC  MOTORS. 

uneven  length  and  resistance.  Fig.  10  shows  a  laminated 
shuttle  armature  of  a  somewhat  improved  form.  The 
stampings  for  the  centre  portion  are  of  the  ordinary 
shuttle  or  H  shape  shown  in  Fig.  11,  while  the  end  stamp- 
ings take  the  shape  shown  in  Fig.  12.  These  are  strung 
on  two  bolts,  and  clamped  together  between  two  castings 
shown  in  side  elevation  by  Fig.  10,  and  in  end  elevation 
by  Fig.  13.  The  wire  is  wound  over  the  central  portion 
or  web,  and  through  the  spaces  at  the  end,  the  shaft 
Leing  driven  securely  into  the  end  castings. 


Fig.  14.— Straight  Pattern  Binding-Post. 


Fig.  15.— Ball  Pattern  Binding-Post. 

Binding-Screws,  etc. — These  are  small  clamps  made 
of  brass,  and  cast  or  turned  in  various  forms  to  suit 
requirements.  They  are  sometimes  called  "  connectors  " 
and  are  used  as  convenient  means  of  connecting  one 
part  of  an  electric  circuit  with  the  rest  of  the  circuit. 
When  made  in  the  form  of  a  pillar  or  post  and  fixed 
by  being  screwed  to  a  base,  they  are  named  "  binding- 
posts."  When  fixed  to  the  two  wires  proceeding  from 
a  generator  of  electricity  so  as  to  form  the  two  poles  of 
the  generator,  they  are  named  "  terminals."  The  ac- 
companying illustrations  will  show  at  a  glance  several 
types  of  binding-screws. 

Fig.  14  shows  a  binding-post  as  used  for  the  terminal 
poles  of  small  dynamo  machines.  When  used  for  this 
purpose  the  post  should  be  massive,  the  threads  on  the 


INTRODUCTION.  19 

screws  well  cut,  and  the  hole  for  the  wire  left  large. 
If  these  posts  are  nickel-plated,  they  enhance  the  ap- 
pearance of  the  machine,  and  require  less  care  to  keep 
them  clean.  Some  makers  taper  the  post  from  the  base 
upward,  whilst  others  round  off  the  tops.  This  is  merely 


Fig.  16. 


Fig.  17. 


Figs.  16  and  1 7.— Telegraph  Pattern  Binding-Posts. 

a  matter  of  taste.  The  wires  from  the  machine  are 
twined  around  the  tang  of  the  post  and  secured  by  a  nut 
beneath  the  base  of  the  machine.  Fig.  15  shows  a  ball 
pattern  binding-post  used  for  a  similar  purpose. 


Fig.  18.— Flat  Base  Terminal. 

Figs.  16  and  17  show  two  "telegraph  pattern"  binding- 
posts.  These  are  used  for  the  terminals  of  telegraph  in- 
struments. When  made  large,  they  are  useful  terminals 
for  ammeters  and  similar  instruments.  Fig.  18  shows  a 
neat  modification  of  the  same  terminal ;  and  Fig.  19 
shows  a  similar  terminal  furnished  with  a  wing  nut. 
This  form  of  nut  may  be  easily  screwed  and  unscrewed 


20          DYNAMOS  AND  ELECTRIC  MOTORS. 

without  the  aid  of  pliers.  It  finds  favour  with 
French  workmen,  and  is  used  by  them  instead  of  the 
milled  head  so  commonly  met  with  in  binding-screws  of 


iff.  20. 
Nut  and  Pin  Terminal. 


Fig.  21.—  Wire  Connector. 


English  makers.  Fig.  20  shows  a  simple  nut  and  pin 
terminal,  as  used  to  insert  in  the  lead  tops  of  carbons 
used  in  Leclanche"  batteries.  Fig.  21  shows  one  form 
of  wire  connector  made  from  brass  tube.  Two  holes 
are  drilled  and  tapped  in  the  side  of  the  tube  to  receive 
two  brass  screws  as  shown  in  the  sketch.  These  con- 
nectors are  useful  when  we  wish  to  join  a  broken 
wire  or  connect  two  wires  together.  Thick  brass  tube 
should  be  used,  or  else  a  lug  should  be  soldered  to  or 
cast  on  the  side  to  thicken  it  where  the  screw  holes 
have  to  be  made,  otherwise  these  will  not  contain 
enough  threads  to  allow  of  the  screws  being  securely 
tightened  on  the  wires. 


CHAPTER    IL 

THE  SIEMENS  DYNAMO. 

IN  1857,  Dr.  Werner  Siemens  invented  the  simple  fo\m 
of  armature  now  known  as  the  Siemens  H  girder,  and 
so  called  because  its  cross-section  resembles  the  section 
of  an  H  iron  girder.  This  is  shown  at  Fig.  8,  p.  15.  As 
this  form  of  armature,  together  with  the  field  magnets, 
is  easily  made,  wound,  and  set  up,  it  has  become  a 
general  favourite.  An  outline  of  the  machine  in 


Fig.  22. — Outline  of  Siemens  Dynamo. 

general  use  is  shown  at  Fig.  22,  whilst  Figs.  23  to  37 
show  in  detail  the  forms  of  its  several  parts.  The 
diagram  Fig.  22  shows  the  position  of  the  parts  com- 
posing the  skeleton,  or  carcase,  of  the  machine  ;  A  being 
the  armature ;  M,  M,  the  pole  pieces ;  c,  c,  the  field 
magnet  cores  ;  and  Y,  the  yoke  to  which  the  field 
magnet  cores  are  attached  by  bolts  or  screws. 

The  field  magnets  are  often  made  to  the  form  shown 
at  Fig.  23,  or  to  that  shown  at  Fig.  24,  in  various  sizes,  to 
suit  the  other  parts  of  the  required  machine,  as  shown 


22          DYNAMOS  AND  ELECTRIC  MOTORS. 

in  the  table  on  p.  24.  They  are  cast  in  soft  iron,  and 
are  sent  out  annealed  ready  for  use.  A  full  set  of 
castings  for  a  Siemens  pattern  machine  of  small  size 
can  be  obtained  for  about  five  shillings,  and  this  will 
make  up  a  5-candle  power  machine.  The  castings  for  a 
machine  of  120-candle  power  will  cost  about  thirty-five 
shillings.  All  castings  received  from  vendors  of  these 
things  are  in  the  rough  as  they  come  from  the  foundry, 
unless  otherwise  ordered,  and  an  additional  price  has  to 
be  paid  for  the  labour  of  shaping  and  fitting  them  ready 


Fig.  23.  Fig.  24. 

Forms  of  Field  Magnets  for  Undertype  Dynamos. 

for  winding  on  the  wire.  Supposing,  however,  that  the 
castings  are  received  in  the  rough,  we  will  set  about 
preparing  the  field  magnet  castings.  These  should  be 
soft  enough  to  file  easily,  or  they  are  unsuited  for  our 
purpose. 

The  first  job  will  be  to  clean  and  true  up  the  parts— 
that  is,  remove  any  rough  ridges  or  lumps  of  iron 
left  on  the  edges  of  the  armature  tunnel.  This  may 
be  done  in  a  lathe  or  by  means  of  a  half-round  coarse 
file.  The  two  castings  for  the  field  magnets  must  be  a 
pair,  and  when  stood  side  by  side  on  a  level  bench,  the 
armature  tunnel  between  them  should  be  of  regular 


THE  SIEMENS  DYNAMO.  23 

form  throughout,  the  cores  of  one  height  and  size,  and 
parallel  with  each  other  when  upright.  If  slight  irregu- 
larities appear  on  the  sides  of  the  tunnel,  take  them  off 
with  the  rounded  face  of  the  file.  The  corners  of  the 
cores  should  also  be  filed  round  and  smooth,  to  prevent 
abrasion  of  the  covering  on  the  wire  whilst  these  are  being 
wound.  If  the  castings  are  shaped  as  shown  at  Fig.  23, 
holes  must  be  drilled  and  tapped  in  the  top  at  a,  6, 
to  receive  screwed  studs  to  hold  the  yoke  in  its  place  on 
the  field-magnet  cores.  Holes  about  \  in.  diam.  must 
also  be  drilled  in  the  lugs  at  c,  d,  e,  /,  to  receive  screwed 
studs  or  small  bolts  securing  the  armature  bearings  to 


Fig.  25. — Solid  H-girder  Armature  commencing  to  wind. 

the  lugs.  Two  larger  holes  must  also  be  drilled  in  tho 
feet  of  the  castings  at  g,  h,  to  receive  short  coach  screws 
used  for  bolting  the  castings  to  their  wood  base. 

The  yoke  to  connect  the  field  magnets,  shown  at  Y 
Fig.  22,  is  a  rectangular  piece  of  iron  plate,  and  must 
be  bedded  on  the  top  of  the  field  magnets'  cores  to  hold 
them  in  the  position  In  the  small  Siemens  machines 
supplied  by  some  makers  this  separate  yoke  is  dis- 
pensed with,  as  the  top  of  one  of  the  castings  projects 
sufficiently  to  bridge  over  the  space  between  the  two, 
and  thus  forms  the  yoke.  In  the  castings  supplied  by 
others,  also,  the  two  projections  have  turned-up  flanges, 
as  shown  at  Fig.  24,  and  these  are  bolted  together. 
The  two  field  magnets  must  be  connected  in  this  or  in 
a  similar  way  by  an  iron  bridge,  so  as  to  form  a  horse- 
shoe magnet,  between  the  poles  of  which  the  armature 
will  revolve. 

The  armature  of  the  solid  H-girder  form  used  in 


DYNAMOS  AND  ELECTRIC  MOTORS. 


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THE  SIEMENS  DYNAMO. 


machines  is  shown  at  Fig.  25.  It  is  a  casting  of 
specially  soft  iron,  and  is  supplied  with  the  other 
castings  for  the  machine.  The  channel  for  the  wire 
should  be  true  and  smooth,  and  the  ends  of  the  web 
should  be  rounded  and  smoothed  to  prevent  abrasion 
of  the  wire  covering.  The  rounded  faces  of  the  cheeks 
must  also  be  free  from  lumps,  and  they  must  also  be 
true  from  end  to  end.  The  ends  must  "be  filed  or  turned 
true  to  form  faces  for  the  spindle-holders  shown  at  Figs. 
26  to  28.  These  are  secured  to  the  ends  of  the  armature 
by  screwed  studs,  and  holes  must  be  drilled  and  tapped 
to  receive  them. 


Fig.  26.  Fig.  27.  Fig.  23. 

Fig.  26.— Spindle  Holder  :  End  View.  Fig.  27.— Section  of 
Spindle  Holder.  Fig.  28.— Section  of  Spindle  Holder 
and  Commutator. 

In  larger  machines,  the  armature  is  built  up  of  purch- 
ings  of  sheet-iron  shaped  as  shown  at  Fig.  11  (p.  17),  or  as 
shown  at  Fig.  29.  These  stampings  are  sold  at  prices 
ranging  from  3s.  b'd.  to  10s.  per  gross,  according  to  size. 
The  stampings  are  strung  on  a  steel  spindle,  as  shown 
at  Fig.  30,  and  secured  at  each  end  by  nuts,  so  as  to 
pinch  the  whole  series  of  plates  between  them.  The 
result  is  to  form  a  channel  for  the  wire,  and  faces 
for  the  cheeks  of  the  armature,  similar  to  that  of  the 
solid  H-girder  form.  This  laminated  form  lessens  the 
tendency  of  the  armature  to  heat  by  generating  cross 
currents  in  itself  whilst  working.  The  laminations  are 
separated  from  each  other  by  varnish  or  paper,  and 
these  help  to  keep  the  armature  cool.  The  spindle 
should  be  long  enough  to  pass  through  the  end  bearings. 

The  spindle-holders  for  the  solid  form  of  armature 
are  made  o/  brass,  either  cast  with  a  projecting  boss, 


2 6          DYNAMOS  AND  ELECTRIC  MOTORS. 

or  made  up  of  a  disc  of  brass  with  a  piece  of  brass 
tube  fitted  in  the  centre  to  give  holding  power  on 
the  [spindles.  The  spindles  should  be  of  steel,  turned 
true  and  smooth,  and  fitted  tightly  in  their  respective 
holders.  The  projecting  bosses  of  these  spindle-holders 
running  against  the  bearings  prevent  end  shake  of  the 
armature  ;  but  when  a  laminated  armature  is  employed, 
the  ends  of  the  spindle  may  be  turned  down  a  little  to 
form  a  shoulder  for  this  purpose. 

The  armature  bearings  for  the  smaller  sizes  of 
machines,  are  cast  in  gun-metal  to  the  form  shown  at 
Figs.  31  and  32,  or  cut  from  sheet  brass  to  the  form  shown 


Fig.  29. — Laminated  Fig.  30. — Iron  Laminations 
Iron  Punching  strung  on  Spindle  to 

for  Shuttle  form   Shuttle 

Armature.  Armature. 

at  Fig.  36  (p.  30),  aud  are  secured  to  the  ends  of  the  field 
magnets  by  long  bolts  resting  in  the  slots  shown  in  the 
lugs,  Fig.  24.  As  the  bolts  run  the  whole  length  of  the 
sides  of  the  machine,  they  then  clamp  the  front  and  back 
bearings  together.  The  bearings  for  the  other  forms  are 
similarly  made,  but  they  are  secured  to  the  lugs  of  the 
field  magnets  by  screwed  studs,  or  by  small  bolts  passing 
through  holes  drilled  in  the  lugs.  Whichever  form  of 
bearing  is  employed,  or  however  it  may  be  secured  to 
the  machine,  the  holes  must  be  exactly  in  the  centre  of 
the  armature  tunnel,  so  that  the  cheeks  of  the  armature 
may  run  no  nearer  to  one  side  than  to  the  other. 

The  field  magnets  may  now  be  bolted  together, 
the  bearings  put  on,  and  the  running  of  the  armature  in 
its  tunnel  tested.  It  should  be  centred  so  as  to  leave 
about  -^o  of  'an  inch  of  space  between  the  cheeks  of  tlio 
armature  and  the  sides  of  the  tunnel.  A  space  the 


THE  SIEMENS  DYNAMO.  27 

thickness  of  stout  brown  paper  is  enough,  but  if  the 
space  is  less  than  this,  the  cheeks  may  bind  against 
the  sides  of  the  tunnel.  If  excessive  space  is  allowed, 
part  of  the  energy  will  be  lost.  If  there  appears  to 
be  a  danger  of  the  armature  touching  the  sides  at  any 
particular  part,  mark  the  place,  and  ease  it  with  a  file. 
A  very  effective  way  to  test  the  running  of  the  armature 
is  to  paste  a  piece  of  paper  over  the  cheeks,  and  then 
revolve  it  in  the  tunnel.  On  taking  it  out  carefully, 
the  abrasions  on  the  paper  will  mark  the  prominent 
parts,  and  these  may  then  be  eased. 

This  form  of  armature  is  wound  with  only  one  coil 
of  wire;;  the  commutator  will  be  a  "  two-part  commu- 
tator "  (see  Fig.  33)— that  is,  one  divided  into  two  sec- 
tions, one  for  each  end  of  the  wire  coil.  These  sections 
must  be  insulated  from  each  other,  and  must  also  be 
insulated  from  the  rest  of  the  machine.  The  cheapest 
and  handiest  insulating  substance  available  is  boxwood 
well  soaked  in  melted  paraffin.  Ebonite  or  vulcanised 
fibre  will  also  serve  the  purpose,  but  these  are  more 
costly.  Therefore  get  a  chunk  of  boxwood  out  of 
which  can  be  turned  a  disc  \\  in.  in  diameter  and 
about  1  in.  thick.  Turn  this  up  true,  with  a  hole  bored 
exactly  in  the  centre  to  fit  tightly  when  driven  on  one 
of  the  spindles.  Then  get  a  piece  of  brass  tube  1  inch 
in  length,  that  exactly  fits  over  the  boxwood,  and  force 
it  tightly  on.  The  smallest  sized  machines  take  a  com- 
mutator I  in.  in  diameter. 

If  now  this  brass-bound  boxwood  disc  were  forced  on 
the  spindle  as  shown  at  Fig.  28,  it  might  work  loose  in 
time;  so,  to  prevent  it  from  slipping,  turn  down  the 
hub  of  the  spindle-holder  enough  to  get  a  good  face 
for  the  boxwood  boss  to  fit  against,  then  bore  two  J  in. 
holes  in  the  holder,  and  fit  them  with  two  short  brass 
pins.  When  we  have  determined  how  the  commutator 
shall  go  on  the  spindle,  two  shallow  holes  may  be 
bored  in  the  inside  face  of  the  boxwood  disc  to  fit 
those  pins  exactly,  and  so  keep  it  from  slipping. 
The  ring  of  brass  must  now  be  divided,  and  upon  the 


2S  Dl'XAMVS   AND   ELECTRIC    MOTORS. 

way  this  is  done  will  depend — all  other  parts  being  right 
—the  proper  working  of  the  machine.  If  divided  into 
two  equal  sections,  by  sawing  straight  across  the  tube, 
the  current  from  the  armature  would  be  interrupted 
abruptly,  and  sparks  would  be  caused,  which  would 
soon  burn  away  the  brass  ring  and  also  the  brushes. 
The  saw-cut  must  therefore  be  made  obliquely  or 
diagonally  across  the  ring. 

But  here  we  must  guard  against  making  the  division 
as  shown  at  A  on  the  left  in  Fig.  34,  for  this  would  be  too 
oblique,  and  the  interruptions  would,  in  consequence, 


Fig.  31.  Fig.  32. 

Bearings  for  Armature.      Fig.  31.— End  View 
Fig.  32.— Section. 

not  take  place  at  the  proper  time.  To  obtain  the 
proper  direction  for  this  saw-cut,  turn  the  disc  on 
one  end  and  draw  a  line  diameterways  across  the  centre, 
and  i  in.  on  each  side  of  this  line  draw  two  other 
lines.  Now  scribe  two  lines  on  one  side  of  the  brass 
exactly  in  a  line  with  the  two  lines  on  the  end.  Turn 
the  disc  over,  and  scribe  two  similar  lines  across  the 
opposite  side.  Now  on  both  sides  scribe  a  line  across 
the  space  between  these  two  lines,  from  the  right- 
hand  end  of  the  top  line  to  the  left-hand  end  of  the 
bottom  line.  Next,  drill  and  countersink  two  small 
holes  on  each  side  of  the  line  to  receive  two  very 
small  brass  screws,  as  shown  at  Fig.  34  (B),  and  put  in 
the  screws,  which  must  not  touch  the  spindle  when 
driven  well  home.  When  this  has  been  done,  the  ring 
may  be  divided  by  sawing  it  through  to  the  boxwood 


THE  SIEMENS  DYXAMO.  29 

on  both  sides  along  the  diagonal  lines,  using  a  hack-saw 
for  the  purpose. 

The  saw-kerf  should  be  widened  a  little,  and  cleaned 
out  well  with  a  thin  file,  or  it  is  apt  to  get  choked 
and  bridged  with  fine  particles  of  metal  worn  from  the 


Fig.  33. — Brass  Ring  for  Commutator. 

brushes.  The  holes  for  the  fixing-pins  may  now  be 
bored,  and  the  commutator  fixed  in  its  place  on  the 
spindle,  having  placed  it  so  that  the  saw-cut  in  the 
commutator  ring  shall  be  on  the  side  of  the  coil 
nearest  the  left-hand  cheek  of  the  armature.  Two 


Fig.  34. —  Commutator,  showing  Divided  Brass  Ring 
and  Screws. 

small  holes  may  now  be  drilled  through  the  spindle- 
holder  (as  shown  at  A,  B,  Fig.  26,  p.  25).  These  are  bushed 
with  ivory  or  some  other  non-conductor,  and  the  ends  of 
the  armature  coil  wire  to  come  through  these  are  securely 
fastened  to  the  commutator  ring. 

The  brushes  are  long  thin  pieces  of  springy  brass, 
copper,  or  phosphor  bronze  fixed  on  each  side  of  the 
commutator  to  brush-blocks  insulated  from  the  rest  of 
the  machine.  Their  duty  is  to  pick  up  the  impulses 


3° 


DYNAMOS  AND  ELECTRIC  MOTORS. 


of  the  interrupted  armature  current  from  the  com- 
mutator sections,  and  convey  those  impulses  to  the 
field  magnet  coils  and  to  the  outer  circuit.  In  the 
machines  of  some  makers  the  brushes  are  attached  to 
boxwood  blocks  fixed  to  the  bearings  of  the  armature 


Fig.  35. — Section  of  Complete  Armature. 

spindle  (as  shown  at  Fig.  36) ;  in  other  machines  they 
are  attached  to  brass  pillars  screwed  into  the  wooden 
base  of  the  machine  on  each  side  of  the  commutator. 
Probably,  for  small  machines,  wooden  blocks  as  shown 
at  Fig.  36,  with  an  adjustable  brush -holder  attached 


Fig.  36.— Commutator  Bearing,  showing  Position  of  Brushes. 


Fig.  37.— Brush  Clamp. 

to  each  block,  are  the  best.  With  the  brushes  fixed,  as 
they  often  are  in  small  machines,  their  adjust- 
ment becomes  a  tedious  task.  The  brush-holder  need 
be  only  a  small  brass  bracket  with  a  set-screw,  as 
shown  at  Fig.  37.  The  brushes  can  then  be  shifted 
to  and  fro,  and  adjusted  at  any  angle  required  by 
placing  wedges  of  brass  in  the  clamps  above  or  below 
the  back  ends  of  the  brushes. 


THE  SIEMENS  DYNAMO.  31 

A  very  good  material  for  the  brushes  of  small 
machines  is  fine  wire  gauze  cut  into  strips,  and  two  or 
three  thicknesses  soldered  to  the  ends  of  stout  brass 
springs  to  ensure  proper  pressure  on  the  commutator. 
Three  forms  of  brushes  in  general  use  are  shown  at  Figs. 
38, 39  and  40.  That  shown  at  Fig.  38  is  merely  a  piece  of 
thin  spring  brass,  shaped  as  shown,  and  fixed  to  a  pillar 
brush-holder.  This  is  an  objectionable  form,  as  it 
often  gets  out  of  order  by  wear,  and  cannot  be  replaced 
or  adjusted  easily.  Fig.  39  is  an  improvement  on  this 
form.  It  is  composed  of  thin  sheet  brass  or  hard 


Fig.  38. 


Fig.  39.  Fig.  40. 

Figs.  38  to  40.— Forms  of  Commutator  Brushes. 

hammered  copper  cut  to  the  form  shown,  with  one  end 
slit  into  fingers  to  the  length  of  2  or  2|  in.,  and  a  slot 
cut  in  the  other  end  to  facilitate  adjustment  The 
fingers  soon  wear  away,  and  must  then  be  replaced.  The 
brush  shown  in  Fig.  40  consists  of  a  piece  of  hard  spring 
brass,  to  one  end  of  which  is  soldered  a  pad  of  copper 
wire  gauze.  This  bears  on  the  commutator,  and  is 
kept  in  contact  with  it  by  the  strip  of  spring  brass  to 
which  it  is  soldered,  the  strip  being  curved  as  shown  at 
Fig.  36  for  this  purpose.  This  pad  is  most  effective  as 
a  brush  ;  it  does  not  cut  away  the  commutator  like 
spring  brass  and  copper,  and  it  is  easily  adjusted  or 
replaced  if  fixed  in  a  brush-block  with  clamp,  as  shown 
at  Fig.  37. 

The  position  of  brushes  for  shuttle  or  H -girder  arma- 
tures is  a  matter  of  considerable  importance.  It  does 
not  matter  how  the  commutator  is  fixed  to  the  shaft  ; 
that  point  is  settled  by  the  most  convenient  way  of 
holding  the  brushes.  But  the  rule  that  must  be  observed 


32          DYNAMOS  AND  ELECTRIC  MOTORS. 

is  that— When  the  two  cheeks  of  the  armature  are 
electrically  opposite  the  two  pole-pieces  of  the  field, 
the  brushes  must  rest  on  the  insulating  strips  on  the 
commutator. 

In  Fig.  41  this  position  is  shown  by  the  brushes  in 
dotted  lines  ;  but  in  practice  the  brushes  are  given  a 
slight  "  lead  "—that  is,  they  are  moved  forward  through 
a  small  angle  in  the  direction  in  which  the  commutator 
moves.  This  brings  the  brushes  on  the  insulating  strips, 
not  when  the  cheeks  of  the  armature  exactly  face  the 
pole-pieces,  but  just  a  little  after  they  have  passed  the 
centre  line. 


Fig.  41.— rosition  of  Brushes  for  Shuttle  Armature. 

The  brushes  with  this  lead  are  shown  in  Fig.  41  in 
full  black  lines,  with  a  centre  line  showing  the  angle 
through  which  they  have  been  turned.  The  exact 
amount  of  this  lead  can  only  be  found  when  the 
machine  is  at  work,  for  some  armatures  require  more 
than  others ;  for  instance,  a  rather  hard  solid  shuttle 
armature  may  require  more  lead  than  one  built  up  of 
separate  punchings.  The  brushes  should  have  just 
enough  lead  for  the  machine  to  give  its  full  current 
without  sparking.  Just  a  trifle  too  much  or  too  little 
lead  may  easily  bring  about  sparks,  which  not  only 
mean  waste  of  power,  but  also  eat  away  both  brushes 
and  commutator,  and  should  therefore  be  avoided.. 

Before  winding  the  armature,  see  that  the  channel  is 
free  from  lumps,  and  the  ends  of  the  web  are  smootlj 


THE  SIEMENS  DYNAMO.  33 

Then  cut  a  strip  of  silk  large  enough  to  envelop  the  web, 
and  coat  this  with  good  shellac  varnish.  Lay  the  silk 
evenly  to  form  a  bed  for  the  wire,  and  varnish  the  silk 
and  the  channel,  and  when  the  varnish  is  dry  proceed  to 
wind  on  the  wire.  This  will  be  all  the  better  for  the 
purpose  in  hand  if  it  has  been  previously  soaked  in  hot 
melted  paraffin.  Commence  winding  as  shown  at  Fig.  25, 
p.  23,  lay  each  coil  evenly,  as  a  reel  of  cotton  is  wound, 
and  wind  close  and  tight,  until  the  required  amount  of 
wire  has  been  wound  on.  The  wire  coil  must  not  stand 
above  the  cheeks  of  the  armature.  If  a  stray  layer 
stands  up  above  the  others,  and  threatens  to  knock 
against  the  sides  of  the  field  magnet  tunnel  whilst  being 
revolved,  it  must  be  pressed  into  its  place  with  a  piece  of 
smooth  wood.  Then  bring  the  two  free  ends  to  one  end 
of  the  armature,  put  on  the  spindle-holder  (Fig.  26,  p.  25), 
bring  the  ends  through  the  ivory-bushed  holes  A  and  B 
made  for  this  purpose,  put  on  the  commutator,  and 
solder  the  two  ends  of  the  coil  to  the  two  sections  of 
the  commutator.  Then  put  on  the  other  spindle- 
holder,  and  the  armature  is  complete.  Fig.  35,  p.  30, 
shows  a  section  of  the  armature  thus  finished.  It  is 
lettered  as  follows : — w,  web  of  armature ;  E,  spindle- 
holders  ;  c,  commutator ;  s  s,  shaft  or  spindle  ;  and  p, 
driving  pulley. 

Whilst  winding  the  wire  on  the  armature  or  the  field 
magnets  of  a  dynamo,  great  care  must  be  exercised  to 
get  each  coil  of  wire  close  to  its  neighbour,  and  each 
layer  of  wire  regular  and  close  to  the  layer  beneath,  for 
on  this  will  depend  the  full  efficiency  of  the  machine. 
Slack  and  irregular  winding  will  cause  loss  of  power, 
and  this  is  specially  observable  in  the  winding  of  the 
armature,  where  cross  winding  will  not  only  prevent  a 
maximum  number  of  coils  being  got  in  a  given  space,  but 
will  also  cause  cross  currents  in  the  wires.  Nevertheless, 
whilst  giving  all  attention  to  the  tightness  and  snugness 
of  the  winding,  it  is  possible  to  be  too  zealous  in  this 
direction,  and  fall  into  the  more  serious  error  of  pulling 
the  wire  so  tightly  over  the  iron  ends  of  the  armature  as  to 


34          DYNAMOS  AND  ELECTRIC  MOTORS. 

cause  the  iron  to  cut  into  the  covering  of  the  wire.  One 
such  abrasion  of  the  covering,  however  small,  will  render 
the  machine  useless,  as  electrical  contact  will  be  made 
through  the  iron  of  the  machine  as  well  as  through  its 
wire  coils. 

Such  accidents  as  these  are  of  frequent  occurrence, 
and  to  detect  them  it  is  necessary  to  have  a  small 
galvanometer,  or  current  detector,  and  with  it  to  test  the 
insulation  of  the  covering  as  the  winding  proceeds. 
Almost  any  price  may  be  paid  for  a  galvanometer,  from 
2s.  6d.  up  to  £10,  according  to  the  value  of  material  and 
workmanship  in  the  instrument ;  but  a  plain  and  simply 
constructed  one,  good  enough  for  this  purpose,  can  be 
got  for  10s.,  or  perhaps  less.  To  test  the  wire  for  com- 
plete insulation  whilst  winding,  connect  a  free  end  of 
it  to  one  stud  of  the  galvanometer ;  connect  the  other 
stud  to  one  terminal  of  a  good  battery  (one  cell  of  a 
Bunsen  or  a  bichromate  will  do  very  well),  and  attach  a 
length  of  copper  wire  to  the  other  terminal  of  the 
battery.  With  the  end  of  this  wire  touch  the  bare  iron 
of  any  part  of  the  armature  (or  of  the  field  magnets 
whilst  winding  them).  If  the  needle  of  the  galva- 
nometer is  deflected,  it  may  be  taken  for  granted 
that  the  wire  covering  is  abraded,  and  each  coil  must 
be  unwound  until  the  faulty  place  is  discovered. 
Such  faults  are  best  repaired  with  a  thread  of  un- 
spun  silk  or  soft  darning-cotton,  soaked  in  melted 
paraffin  and  wound  around  the  abraded  spot.  If  the 
galvanometer  needle  does  not  move  at  all  when  the 
iron  is  touched  with  the  battery  wire,  we  may  be  fairly 
certain  that  the  coil  is  insulated  from  the  iron  of  the 
field  magnet  core,  or  of  the  armature,  as  the  case  may  be. 

Greater  care  is  needed  in  winding  a  laminated  arma- 
ture than  in  one  having  a  solid  core,  since  the  edges  of 
the  end  plates  are  liable  to  cut  through  the  protecting 
coat  of  silk  and  covering  of  the  wire  if  this  is  pulled  too 
tightly  over  the  edges.  Some  little  difficulty  also  will  be 
experienced  in  getting  the  coils  of  wire  to  lie  close  to  the 
spindle  whilst  winding  them  on  one  side.  This  may  be 


THE  SIEMENS  DYNAMO.  35 

overcome  by  tying  each  coil  back  with  a  short  piece  of  tape, 
until  the  curvature  of  the  spindle  has  been  passed  In 
winding  a  laminated  H-girder  armatumfora  Manchester 
field,  the  coils  may  be  prevented  from  slipping  at  the 
ends  by  bending  forward  two  of  the  laminated  plates  at 
each  end,  so  as  to  form  two  flanges,  against  which  the 
coils  can  rest  as  against  the  sides  of  the  end  slot  in  a 
solid  armature.  As  there  are  no  spindle-holders  through 
which  to  pass  the  ends  of  the  coil  we  have  to  fasten 
them  direct  to  the  sections  of  the  commutator,  to  the 
inside  edgea  of  which  they  should  be  secured  by  solder. 
It  will  also  be  advisable  to  tie  the  ends  down  to 
the  spindle  with  a  few  turns  of  tape,  to  prevent  the 
outer  coil  from  shaking  loose  in  working. 

Before  winding  the  field  magnet  cores,  it  will  be  neces- 
sary to  prepare  them  for  the  wire  by  wrapping  around 
them  a  layer  of  silk  ribbon  well  soaked  in  melted  paraffin, 
applied  to  the  iron  warm,  and  then  made  quite  smooth. 
The  wire  should  also  be  prepared  for  winding  by  first 
dividing  the  allotted  quantity  into  two  equal  parts, 
making  these  into  hanks  or  coils  large  enough  to  go  loosely 
over  a  two-gallon  stoneware  jar,  and  then  well  soaking 
them  in  melted  paraffin.  The  wire  for  the  dynamos 
specified  in  the  table  on  p.  24  may  be  divided  by 
measurement,  if  it  is  found  inconvenient  to  divide  it  by 
weight,  if  we  remember  that  No.  22  S.W.G.  d.c.c.  copper 
wire  measures  125  yards  in  the  Ib.  The  wire  may  be 
wound  on  by  hand  if  the  worker  is  unprovided  with 
suitable  apparatus,  but  it  can  be  wound  more  regularly, 
smoother,  and  tighter  in  a  lathe,  or  by  means  of  a  special 
winder,  which  can  be  easily  and  cheaply  made  up  for 
the  purpose  from  a  few  scraps  of  wood,  a  few  bolts,  and 
a  winch-handle.  Centre  the  field  magnet  casting  in  the 
lathe,  and  when  it  runs  true,  proceed  to  wind  on  the 
wire. 

If  the  hank  of  wire  has  been  placed  over  a  glazed 
stoneware  bottle  filled  with  water,  the  coils  will  slip  off 
easily  as  the  wire  is  wound  on  the  casting.  Commence  at 
the  channel  or  bottom  end  of  the  core  ;  wind  some  seven 


3 6          DYNAMOS  AND  ELECTRIC  MOTORS. 

or  eight  inches  of  the  wire  on  a  pencil  to  form  a  close 
spiral,  to  be  stretched  out  after  winding  to  form 
connections.  Lay  this  close  to  the  bottom  end,  take 
one  turn  around  the  casting,  and  secure  the  spiral 
to  this  turn  with  a  piece  of  strong  twine.  Wind 
on  the  coils  evenly  side  by  side,  and  when  within  two 
inches  of  the  end,  lay  in  two  four-inch  lengths  of  tape 
under  the  last  few  coils  on  the  outside  of  the  core, 
leaving  the  ends  hanging.  Before  winding  back  with 


Fig.  42. — Siemens-type  Dynamo  complete. 

the  next  layer,  bring  the  ends  down  over  the  first 
layer,  and  thus  secure  the  last  few  coils  of  the  first 
layer  from  slipping  away  under  the  pressure  of  the 
next.  If  the  ends  of  each  layer  are  thus  bound, 
there  will  be  no  danger  of  the  top  layer  sinking  in 
between  the  coils  of  that  beneath  it. 

When  all  the  wire  has  been  wound  on,  tie  the 
free  end  to  one  of  the  coils,  or  to  the  core,  with  a 
piece  of  stout  twine.  Serve  the  other  field  magnet 
core  in  a  similar  manner,  testing  each  layer  for  insula- 
tion as  the  work  proceeds  ;  then  coat  the  outer  wires 
with  a  layer  of  sealing-wax  varnish,  and  set  them  aside 
to  dry.  As  the  cores  of  some  forms  of  field  magnets 


THE  SIEMENS 


37 


are  unprovided  with  flanges,  this  method  of  taping 
just  described  will  be  found  very  convenient  in  pre- 
venting slipping  of  the  end  coils;  but  flanges  are 
preferable  where  these  can  be  introduced,  as  they 
not  only  prevent  slipping  but  also  protect  the  coils 
from  possible  injury. 

The  various  parts  having  been  prepared,  they  must 


Fig.  43.— Magnetising  Field  Magnets. 

now  be  fitted  together.  It  is  well  known  that  a  straight 
bar  magnet  has  two  opposite  poles— one  at  each  end. 
One  of  these  is  called  the  north  pole  of  the  magnet, 
its  opposite  being  the  south  pole.  If  now  we  bend  the 
bar  in  the  shape  of  a  horse-shoe,  the  two  poles  are 
brought  near  each  other,  but  they  still  preserve 
their  characteristic  opposite  polarities. 

If  we  wind  an  insulated  copper  wire  around  a  straight 
bar  of  steel  or  of  iron  as  in  the  left  half  of  Fig.  43,  and  send 
an  electric  current  in  the  direction  of  the  arrow,  through 
the  wire,  we  shall  find  that  the  lower  end  N  of  the 

434360 


-^ 

38          DYNAMOS  AND  ELECTRIC  MOTORS. 

iron  or  steel  bar  has  assumed  a  north  magnetic  polarity, 
and  at  the  same  time  its  opposite  end  s  has  a  south 
magnetic  polarity.  If  an  iron  bar  be  bent  into  the 
shape  of  a  horse-shoe  with  the  wire  on,  it  will 
then  resemble  the  two  field  magnets  of  Fig.  43, 
with  space  between  the  legs  in  which  the  armature 
may  revolve.  The  two  field  magnets  are  wanted, 
with  a  north  pole  on  one  side  of  the  armature 
and  a  south  pole  on  the  other  side.  As  both  of 
the  cores  have  been  wound  from  the  bottom  or 
channel  end,  it  follows  that  if  we  send  a  current 
through  each  separately  in  the  same  direction  in  which 
they  are  wound,  the  two  bottom  cheeks  would  be 
both  north  poles,  and  if  we  connected  the  finishing  end 
of  one  coil  of  wire  with  the  commencing  end  of  the 
other,  we  should  realise  the  same  result ;  but  if  we 
connect  together  the  two  finish  ends  of  the  coils,  as 
shown  at  Fig.  43,  and  send  a  current  from  the  left- 
hand  end  to  the  right,  it  will  enter  at  N,  traverse 
the  coils  in  the  direction  shown  by  the  arrow,  leave 
at  s,  cross  over  to  the  right-hand  core,  and  traverse 
its  coils  in  the  opposite  direction,  thus  producing  a 
south  pole  at  the  bottom  and  a  north  pole  at  the  top. 

Connect  one  or  two  quart  Bunsen  or  bichromate 
cells  to  the  coils,  taking  care  to  join  the  carbon  of 
the  battery  with  N  on  the  left,  and  the  zinc  of  the 
battery  with  s  on  the  right.  As  the  current  in  a 
battery  may  be  supposed  to  start  from  the  zinc  and 
move  through  the  liquid  towards  the  other  element, 
we  can  by  this  means  always  ensure  sending  a  current 
in  the  right  direction.  When  thus  magnetised,  the 
field  magnets  may  be  connected  together  and  the 
machine  fitted  together. 

The  field  magnets  are  fastened  securely  together  by 
the  yoke  at  the  top,  but  to  ensure  proper  rigidity  and 
stability  to  the  machine,  they  must  also  be  firmly 
secured  to  a  thick,  well-seasoned  board  of  oak,  teak, 
walnut,  or  mahogany  by  short  coach  screws  passing 
through  the  lower  outstanding  flanges.  This  board 


THE  SIEMENS  DYNAMO.  39 

may  be  trimmed  at  the  edges,  planed,  and  polished, 
to  ensure  a  finished  appearance.  The  complete  machine 
is  illustrated  at  Fig.  42,  p.  36. 

From  the  simplicity  of  its  design,  this  type  of 
machine  lends  itself  readily  to  illustrate  how  the  wires 
of  a  dynamo  should  be  connected.  Figs.  44  and  45 
show  two  distinct  methods  of  connecting  the  wires.  The 


Fig.  44.— Diagram  of  Series 
Connections. 


Fig.  45.— Diagram  of  Shunt 
Connections. 


method  shown  by  the  full  lines  at  Fig.  44  is  called  con- 
necting as  a  series  machine — that  is,  the  field  magnets, 
the  armature,  and  the  outer  circuit  may  be  regarded  as 
three  cells  of  a  battery,  and  the  whole  connected  up 
one  after  the  other  in  one  circuit.  No  current  can 
pass  through  the  field  magnet  coils  until  the  outer 
circuit  is  completed.  When  one  end  of  the  field 
magnet  wires  is  connected  to  the  brush  A,  and  the 
other  end  to  the  brush  B,  as  shown  by  dotted  lines  in 
the  diagram  Fig,  44,  the  machine  will  be  short- 


40  DYNAMOS  AND  ELECTRIC  MOTORS. 

circuited.  But  if  we  break  one  of  the  wires  at  c, 
and  take  it  to  a  binding-screw,  then  take  the  piece 
hanging  to  B,  and  connect  that  to  another  binding- 
screw  as  shown  by  the  full  lines,  the  two  screws  will 
form  the  two  poles  of  the  machine,  to  which  the 
wires  from  the  outer  or  working  circuit  must  be 
attached.  This  method  of  connecting  the  wires  is  only 
suitable  in  special  cases,  as  for  working  arc  lamps. 

Fig.  45  shows  a  method  of  connecting  the  machine 
in  shunt — that  is,  only  part  of  the  current  generated 
in  the  machine  passes  through  the  coils  of  the  field 
magnets.  The  ends  of  the  coils  are  then  connected 
with  the  two  brushes,  and  these  are  both  connected 
with  the  binding-screws  which  form  the  terminal  poles 
of  the  machine.  The  circuit  is  now  divided,  part  of 
the  current  going  through  the  work  in  the  outer 
circuit,  and  part  going  through  the  field  magnet  coils. 
This  is  the  method  of  connecting  occasionally  adopted 
in  dynamos  intended  for  running  incandescent  electric 
lamps,  because  the  electro  motive  force  generated  is, 
within  certain  limits,  kept  constant.  Compound  wind- 
ing, a  combination  of  the  series  and  shunt,  is,  however, 
better  suited  to  this  purpose.  The  letter  references  in 
this  Fig.  correspond  to  those  in  Fig.  44. 


CHAPTER  III 

THE  GRAMME   DYNAMO. 

IN  1871  a  French  electrician  named  Gramme  in- 
vented a  dynamo  in  which  he  used  as  the  armature  a 
ring  of  soft  iron  wires  with  insulated  copper  wire  wound 


Fig.  46. — Gramme  Dynamo  Complete. 

in  sections  over  it.  Although  he  was  not  the  first  to 
use  a  ring  armature  made  of  iron,  he  was  able  to  patent 
this  modification,  which  gave  birth  to  the  form  of 
armature  since  modified  and  altered  in  many  different 
ways,  but  still  known  as  the  Gramme  ring.  The 
patent  expired  in  1884. 

The  many  modifications  of  Gramme's  iron  ring, 
including  the  Gramme  ring  itself,  must,  however,  be 
regarded  as  developments  of  a  discovery  made  in  1860 
by  Dr.  Antonio  Pacinotti,  Professor  at  the  University  of 


42          DYNAMOS  AND  ELECTRIC  MOTORS. 

Pisa,  who  found  that  he  could  make  a  most  efficient 
dynamo  by  employing  as  an  armature  an  iron  wheel 
with  sixteen  cogs,  and  winding  between  the  cogs 
sixteen  coils  of  insulated  copper  wire.  Here,  then, 
was  the  first  ring  armature. 

Some  idea  of  the  general  appearance  of  a  Gramme 
dynamo  will  be  gathered  from  Fig.  46,  which  represents 
a  small  Gramme  machine  complete. 

The  carcase  of  the  Gramme  dynamo  differs  in  form 


Fig1.  47. — Iron  Carcase  of  Gramme  Dynamo. 

and  structure  from  that  of  others.  A  general  idea  of 
it  is  given  in  Fig.  47,  where  s,  s,  represent  the  iron 
standards  or  supports ;  c,  c,  c,  c,  the  field  magnet  cores 
without  flanges  ;  and  M,  M,  the  pole  pieces  between  which 
the  armature  revolves.  Soft  iron  castings  can  be  cheaply 
obtained,  and  as  probably  they  will  be  received  rough  as 
they  come  from  the  foundry,  they  must  be  put  into  shape 
and  fitted  for  use  by  the  dynamo  maker  himself.  The 
first  thing  to  be  considered  and  taken  in  hand  will  be 
the  standards,  one  of  which  is  shown  at  Fig.  48,  fitted 
with  a  bridge  for  the  brush -holders.  It  will  be  seen,  on 
referring  to  Fig.  47,  that  each  standard  has  two  project- 
ing lugs,  one  on  each  side.  The  uses  of  these  are  :  in 


THE  GRAMME  DYNAMO.  43 

one  standard  to  hold  the  bolts  which  support  the  bridge 
of  the  brush-holders,  and  in  the  other  standard  to  hold 
the  terminals  of  the  machine.  The  bridge  for  the  brush- 
rocker  bearing  may  be  one  of  the  iron  castings  sent  with 
the  carcase.  This  must  be  mounted  on  the  face-plate 
of  a  lathe,  the  boss  bored  to  allow  the  spindle  to  pass 
through,  and  turned  on  the  outside  to  hold  the  rocker  of 
the  brush-holder.  In  Fig.  48,  the  holes  F,  F,  above  and 
below  the  bridge  (marked  R)  are  for  the  bolts  of  the 
field  magnet  cores  to  pass  through.  It  is  essential  that 


Fig.  48. — Inner  Face  of  Standard  with  Bridge  for 
Brush-Holders. 


the  flanged  ends  of  the  cores  should  be  in  perfect 
magnetic  contact  with  the  iron  of  the  standards,  so  it 
will  be  advisable  to  surface  the  rough  iron  within  the 
diameter  of  the  core  flanges  shown  in  Fig.  49,  to  form 
bearing  surfaces  for  the  bright  ends  of  the  turned  core 
flanges.  The  other  standard  must  now  be  treated  in  a 
similar  manner,  but  in  this  the  holes  in  the  lugs  will  be 
plugged  with  ebonite,  to  hold  the  terminals.  Holes 
must  be  bored  in  the  feet  of  the  standards,  to  receive 
bolts  for  fastening  the  machine  to  a  bench  or  to  the  floor. 
The  cross-shaped  slots  in  each  standard  are  intended  to 


44          DYNAMOS  AND  ELECTRIC  MOTORS. 

hold  the  brass  bearings,  which  are  fitted  into  the  lower 
portion  of  the  slot,  and  held  in  position  by  small 
wedges. 

The  field  magnet  cores  (Fig.  49)  are  best  cast  in 
one  with  the  cheeks,  or  pole  pieces,  and  the  flanges, 
and  with  a  wrought-iron  bolt  embedded  at  each  end  of 
the  casting  with  the  threaded  part  projecting  as  shown. 
Perfect  contact  is  then  ensured  between  all  the  parts, 
and  this  is  important  in  order  to  maintain  magnetic 
continuity  between  the  pole  pieces  and  the  standards 
which  form  their  yokes.  The  outside  faces  of  the 
flanges  should  be  turned  true  and  bright,  to  ensure  a 
clean  surface  contact.  Both  cores  with  their  pole  pieces 


Fig.  49. — Magnet  Core  with  Flanges  and  Pole  Pieces. 

may  now  be  fitted  to  the  standards,  the  ends  of  the 
projecting  pins  screwed  and  fitted  with  nuts,  and  the 
cheeks  made  to  hang  in  line  with  each  other.  Then 
bolt  the  cores  and  standards  up  tight,  mark  by  small 
nicks  with  a  file  on  flanges  and  standard  the  positions 
of  each  piece,  and  drill  on  each  side  of  the  core  through 
each  flange  |-in  holes  into  the  standards  to  the  depth 
of  i  in.  Iron  pins  fitted  in  these  holes  and  fixed  in  the 
flanges,  will  form  a  guide  in  fitting  the  parts  together 
after  the  cores  are  wound  with  wire,  and  ensure  that 
the  cores  shall  be  placed  in  their  right  position. 

The  armatures  of  small  Gramme  machines  are  not 
now  made  of  iron  wire,  as  in  the  original  machines. 
They  are  now  built  up  of  rings  of  sheet-iron,  shaped 
as  shown  at  Fig.  50,  with  a  number  of  cogs  on  the 
periphery  of  each  ring.  It  will  thus  be  seen  that  the 


THE  GRAMME  DYNAMO.  45 

armature  is  practically  a  Pacinotti  ring  armature.  The 
number  of  cogs  and  intermediary  spaces  are  arranged  on 
each  machine  to  suit  the  designer,  and  may  be  any  even 
number,  such  as  ten,  twelve,  fourteen,  sixteen,  and  so  on. 
In  the  small  machine  shown,  the  number  is  ten,  and 
the  laminations  range  in  thickness  from  fourteen  to 
twenty-five  to  the  inch.  The  method  of  building 
up  is  as  follows  :  small  holes  are  drilled  through 
alternate  cogs  of  each  lamination,  as  shown  at  Fig.  50. 


Fig.  50. — Laminated  Iron  Punching  for  Ring  Armature. 

These  holes  may  be  \  in.  or  f  in.  in  diameter,  but  they 
must  exactly  coincide  with  each  other  through  the  whole 
number  of  plates,  as  they  have  to  admit  rods  on  which 
the  laminated  plates  are  strung.  The  rods  should  be 
of  a  material  of  high  electrical  resistance,  to  avoid 
eddy  currents  in  the  armature  when  at  work  Both 
ends  of  each  rod  may  be  threaded,  and  fitted  with 
suitable  hexagonal  nuts.  Ebonite  bushes  and  washers 
should  be  placed  between  the  nuts  and  the  armature 
spiders  and  plates. 

The  plates  may  next  be  coated  with  good  tough 


46 


DYNAMOS  AND  ELECTRIC  MOTORS. 


varnish,  such  as  Japan  or  Brunswick  black,  and  set  aside 
until  the  varnish  is  dry  and  firm.  They  are  then  strung 
on  the  rods,  and  all  bolted  securely  together  to  form 
one  continuous  wide  ring.  This  ring  must  now  be 
mounted  on  a  support,  which  in  turn  has  to  be  fixed  to 
the  spindle,  whilst  space  must  be  left  between  them  for 
winding  the  coils  of  wire.  This  support,  or  spider,  may  be 
of  brass  or  of  gun-metal,  and  is  generally  sold  with  the 
other  castings.  One  with  five  spokes,  to  suit  a  ten-cogged 


Fig.  51. — Spider  for  Laminated  Ring  Armature. 

armature,  is  shown  at  Fig.  51.  Each  arm  must  have  a 
hole  drilled  in  it  as  shown,  to  fit  the  ends  of  the  rods 
running  through  the  armature  plates.  The  hole  in  the 
centre  must  also  be  bored  true  to  fit  the  spindle,  and  a 
key- way  cut  as  shown.  When  bolting  these  spiders  to  the 
armature,  care  should  be  taken  to  tighten  all  the  nuts 
gradually,  and  so  bring  the  plates  and  spiders  together 
without  straining  the  threads.  This  done,  the  surplus 
thread  should  be  cut  off,  the  ends  of  the  rods 
rounded,  and  each  nut  secured  with  a  touch  of  soft 
solder. 

In  preparing  the  armature  each  space  between  the 


THE  GRAMME  DYNAMO.  47 

cogs  will  be  filled  with  a  coil  of  wire,  wound  by 
passing  one  end  of  it  through  the  space  between 
the  arms  of  the  supporting  spider  and  around  the 
combined  thickness  of  the  laminations,  as  shown  at 
Fig.  52.  As  the  space  inside  is  slightly  less  than  that 
between  the  cogs  there  is  a  danger  of  the  inner  part  of 
one  coil  encroaching  on  the  wire  space  of  its  neighbour. 
To  prevent  this,  wooden  guides  may  be  employed,  fixed 
between  the  cogs  on  the  outside,  and  secured  to  other 
wooden  guides  inside  the  armature  by  suitable  screws 


Fig.  52.— Portion  of  Ring  Armature  ready  for  Winding. 

passing  through  the  ends,  as  shown  at  Fig.  52,  and 
also  in  section  at  A  B,  A  B,  Fig.  50.  These  effectually 
prevent  slipping  of  the  wire  coils  whilst  the  wire  is  being 
wound  on,  and  can  be  moved  from  one  space  to  another 
as  the  work  proceeds. 

Before ;  preparing  the  spindle  for  the  armature, 
it  will  be  advisable  to  fit  the  bearings  in  their 
places  in  the  standards.  These  should  be  fitted  in  the 
lower  part  of  the  crosses  in  the  standards;  the 
cross-slit  receives  an  iron  plate,  fixed  in  with 
wedges,  to  hold  the  bearings  down,  and  the 
upper  part  of  the  cross  forms  a  space  for  the 
lubricator.  The  stem  of  this  lubricator  is  screwed  to  fit 
a  hole  in  the  wedge-plate,  and  the  oil  is  conducted 


48          DYNAMOS  AND  ELECTRIC  MOTORS. 

through  a  hole  in  the  upper  half  of  the  bearings,  which 
are  turned  true,  and  fixed  securely. 

The  spindle  should  be  made  of  mild  steel,  of  a  size 
and  length  suitable  to  the  machine  in  hand,  and  turned 
to  the  shape  shown  at  Fig.  53.  The  left-hand  end  from 
A  to  B  will  run  in  the  left-hand  bearing  of  the  machine, 
shown  at  Fig.  46  (p.  41),  and  carry  the  driving-pulley. 
The  two  shoulders  at  B  and  c  are  for  the  bearing  and  the 
boss  of  the  armature  spider  respectively :  At  D  and  E 
holes  must  be  drilled  through  the  shaft  and  fitted  with 
pins,  which  project  and  fit  the  key-ways  left  in  the 
spiders,  and  thus  prevent  the  armature  from  turning 
round  on  the  spindle.  The  space  between  E  and  the 
screwed  part  at  s  will  be  occupied  by  the  commutator ; 


Fi£.  53. — Armature  Spindle  of  Gramme  Armature. 

the  remainder  of  the  spindle  will  run  in  the  right-hand 
bearing,  Fig.  46. 

A  hexagonal  nut  must  be  fitted  on  the  thread  at  s 
to  bring  the  commutator  and  the  spiders  of  the  arma- 
ture in  close  contact  with  each  other.  The  spindle 
being  prepared,  next  mount  the  armature  on  it,  put  the 
spindle  into  its  place,  and  spin  it  round  to  see  that 
every  part  runs  true,  as  now  will  be  the  time  to  make 
any  alteration  required.  This  done,  with  a  half-inch 
square  file  trim  off  any  roughness  which  may  appear 
on  or  between  the  armature  cogs,  so  as  to  make  the 
whole  smooth.  If  the  cogs  do  not  properly  clear  the 
pole-pieces,  the  projecting  parts  may  be  trimmed  off  in 
a  lathe.  The  spaces  between  the  cogs  should  now  be 
coated  with  varnish  and  the  armature  set  aside  to  dry, 
preparatory  to  being  wound  with  wire. 

The  commutator  is  furnished  with  several  seg- 
ments, corresponding  in  number  with  the  coils  on  the 


THE  GRAMME  DYNAMO. 


49 


armature.  Fig.  54  gives  a  general  idea  of  its  appear- 
ance when  finished,  whilst  Figs.  55  and  56  show  how  it 
is  constructed.  In  the  centre  of  a  piece  of  well- 
seasoned  boxwood,  large  enough  to  turn  out  a  solid  hub 


Fig.  54. —Commutator  for  Ring  Armature  complete. 

of  not  less  than  2  in.  in  length  and  3  in.  in  diameter, 
bore  a  hole  to  fit  the  armature  spindle.  On  this 
cylinder  of  boxwood  mount  the  bars  of  the  commu- 
tator, as  shown  in  Fig.  54.  It  would  be  possible  to 


Fig.  55.— How  to  divide 
Commutator  Ring. 


Fig.  56.— How  to  insulate 
Commutator  Segments. 


cut  out  these  bars  one  by  one  from  a  sheet  of  hard 
brass,  and  fit  each  to  the  outside  of  the  cylinder ;  but 
the  commutators  of  small  dynamos  may  be  built  up  by 
a  more  convenient  and  accurate  method.  Procure  a 
piece  of  gun-metal  tube,  with  sides  quite  \  in.  thick, 
and  of  a  diameter  large  enough  to  fit  over  the  box-wood 
hub,  after  a  light  boring  cut  ha?  been  taken  through  the 


50          DYNAMOS  AND  ELECTRIC  MOTORS. 

inside  to  render  it  smooth.  Cut  off  a  piece  of  the  tube 
long  enough  to  cover  the  hub,  and  fit  it  tightly  on. 
Now  divide  the  ring  into  as  many  equal-sized  sections 
as  there  are  cogs  on  the  armature.  If  there  are  ten 
cogs  have  ten  sections,  if  fourteen  cogs  have  fourteen 
sections,  but  each  section  must  be  equal,  so  as  to  form  a 
series  of  equal-sized  bars  all  round  the  hub.  The 
division  lines  should  be  deeply  marked  with  a  sharp  steel 
scriber,  and  then  nicked  with  a  hack-saw,  as  shown  at 
Fig.  55.  Next  drill  a  small  hole  through  each  end  of 
each  section  and  into  the  hub  beneath  ;  countersink  the 
mouth  of  each  hole,  and  drive  a  short  brass  screw  into 
each,  as  shown  in  Fig.  55.  This  done  all  round,  with 
a  saw  separate  each  section  from  its  neighbour,  and 
allow  the  saw  to  enter  the  boxwood  hub  to  the  depth  of 
nearly  \  in.,  to  form  a  hold  for  the  insulating  substance 
to  be  placed  between  each  section.  The  insulating  sub- 
stance may  be  either  vulcanised  fibre  or  asbestos  mill- 
board. Procure  some  sheet  fibre  or  millboard,  a  trifle 
thicker  than  the  saw-cut  divisions,  and  from  it  cut  slips 
large  enough  to  fill  the  cuts  exactly,  as  shown  by  the 
thick  black  lines  at  Fig.  56. 

Slightly  ease  the  screws  of  each  section,  wedge  the 
prepared  insulating  strips  firmly  into  each  saw-cut,  then 
tighten  the  screws  again,  and  so  pinch  each  strip  tightly 
on  each  side  between  the  edges  of  the  sections.  When 
this  is  done,  mount  the  hub  in  a  lathe,  and  true  up  all 
rough  projecting  parts  with  a  sharp  tool,  or  with  a  rough 
file  at  first  and  then  with  a  smoother  file. 

Each  segment  of  the  commutator  will  have  to  be 
connected  to  the  ends  of  two  coils  of  wire,  and  the  best 
means  of  making  a  connection  is  in  the  following 
manner : — Choose  either  end  of  the  commutator  to  go 
next  the  armature,  and  in  the  extreme  end  of  each  section 
drill  a  -^  in.  hole,  and  tap  each  hole  to  receive  a 
screw.  Next  take  a  length  of  No.  12  S.W.G.  hard  copper 
wire,  and  cut  it  up  into  two-inch  lengths.  Flatten  one  end 
of  each  length  as  shown  at  Fig.  57,  and  screw  the  other 
ends  to  go  into  the  tapped  holes  made  to  receive  them. 


THE  GRAMME  DYNAMO.  51 

Tin  the  screwed  ends  of  each  connector  with  solder, 
and  as  they  arc  done  screw  them  into  their  places, 
giving  each  a  touch  with  the  soldering-bit  to  make  the 
solder  run,  and  fix  the  connector  firmly  in  its  place. 

A  disc  of  vulcanised  fibre,  slightly  larger  in  diameter 
than  the  commutator,  should  now  be  turned  out 
of  a  piece  of  |-in.  sheet  fibre.  This  must  be  placed 
between  the  end  of  the  commutator  and  the  arms  of  the 
armature  spider,  to  ensure  the  complete  insulation  of 
the  one  from  the  other  when  they  are  tightened  up 
on  the  spindle. 

Before  winding  the  wire  on  the  armature,  calculate 
how  much  will  be  needed  for  all  the  coils,  and  divide 
this  quantity  equally  among  them,  to  ensure  each  coil 


Fig.  57. — Copper  Connector  for  Ends  of  Armature  Coils. 

having  the  same  resistance.  A  table  at  the  end  of  this 
chapter  gives  particulars  suitable  to  each  size  of  arma- 
ture. In  this  table  only  three  sizes  are  specified : 
namely,  Nos.  16,  20,  and  22  s.w.G.  By  remembering  that 
No.  1C  cotton-covered  copper  wire  runs  about  25  yards 
in  the  lb.,  No.  20  runs  80  yards  in  the  lb.,  and  No.  22 
runs  120  yards  in  the  lb.,  we  can  easily  calculate  the 
length  of  wire  for  eacli  coil  by  multiplying  the  number 
of  yards  per  lb.  by  the  number  of  Ibs.  to  be  used,  and 
dividing  this  by  the  number  of  coils  to  be  placed  on  the 
armature.  For  instance,  supposing  we  have  to  use  4  Ibs. 
of  No.  20  S.W.G.  on  an  armature  with  10  divisions : — 4  X  80 
=  320  ;  and  this,  divided  by  10  (the  number  of  divisions), 
will  give  32  yards  to  each  division.  Measure  off  the 
length  for  each  coil,  and  roll  the  wire  up  into  hanks,  con- 
taining one  coil  in  each  hank.  Place  each  hank  in  a 
vessel  containing  hot  melted  paraffin,  and  let  it  soak 
for  several  minutes,  then  hang  it  up  to  drain  dry. 

Next    make   a   shuttle   of    tough    hard    wood,  to 


S2  DVXAMOS  AND  ELECTRIC  MOTORS. 

the  shape  shown  at  Fig.  58.  This  shuttle  may  be 
9  in.  in  length,  and  of  a  width  suitable  to  the  size 
of  the  spaces  through  which  it  has  to  pass ;  the  gaps 
in  the  ends  must  also  be  cut  large  enough  to  take 
the  whole  coil  of  wire,  and  this  Avill  vary  with  the 
size  of  the  armature  to  be  wound.  The  shuttle  for  the 
smallest  on  the  list  (on  page  59)  should  measure  9  in. 
X  1  in.  X  i  in.,  and  should  have  gaps  |  in.  deep  by  jj  in. 
in  width.  All  edges  must  be  rounded  and  made  quite 
smooth,  to  prevent  chafing  of  the  cotton  or  silk  cover- 
ing whilst  winding  the  coil.  This  shuttle  must  now  be 
neatly  wound  with  one  of  the  coils  of  wire,  and  then 
we  are  ready  for  transferring  it  to  the  armature. 


Fig.  58. — Wooden  Shuttle  for  winding  Armatures. 

This  is  a  two-handed  job,  and  it  is  necessary  to  have 
a  helper  whilst  doing  it.  The  armature  ring  may  be  held. 
on  a  low  trestle  between  the  winder  and  his  assistant. 
Examine  the  edges  of  the  spaces  between  the  cogs  and 
inside  the  ring,  to  detect  any  rough  places  likely  to 
abrade  the  wire  covering.  If  any  of  these  appear,  do  not 
file  them  down— for  in  so  doing  the  dried  coat  of  shellac 
varnish  would  be  injured— but  cover  them  with  short 
pieces  of  broad  tape,  stuck  on  after  being  well  soaked  in 
hot  paraffin  wax. 

Begin  winding  on  the  left-hand  side  of  one  of  the 
spaces,  next  to  an  arm  of  the  spider.  Wrap  a  few  turns 
of  the  outside  end  of  the  wire  around  the  arm  of  the 
spider,  just  to  hold  it  in  its  place,  pass  the  shuttle  to  the 
assistant  over  the  armature,  and  get  him  to  pass  it  back 
through  the  ring  ;  lay  the  coil  up  close  to  the  left-hand 
cog,  and  draw  it  moderately  tight ;  then  pass  the  shuttle 
over  again  to  the  assistant,  who  will  return  it  through  as 
before  (see  Fig.  52).  Thus  proceed,  laying  each  coil  close 


THE  GRAMME  DryA.\ro.  53 

against  the  one  preceding  it,  until  the  space  between 
the  two  cogs  has  been  covered  by  one  layer.  Then 
wind  back  from  right  to  left  until  this  layer  has  been 
closely  and  regularly  ^covered  with  another  layer.  If 
using  large  wire,  such  as  No.  20  or  No.  16,  there  will  be 
a  tendency  on  the  part  of  each  coil  to  bulge  in  the 
centre  of  the  space.  This  bulging  must  be  kept  down 
from  the  start  by  gently  tapping  the  bulging  part 
(whilst  tightening  the  coil)  with  a  small  wooden 
mallet,  or  by  placing  a  piece  of  wood  on  the  wire, 
and  striking  the  wood  with  a  hammer.  The  wire 
must  be  kept  level  and  compact  in  the  outside 
space,  but  in  the  inside  this  may  be  disregarded. 
Whilst  winding  the  coil  test  it  frequently  for  insulation, 
and  make  good  each  fault  before  going  on  further, 
for  leakage  here  will  destroy  the  efficiency  of  the 
machine.  When  the  first  coil  has  been  wound,  leaving 
the  wire  ending  on  the  side  of  the  space  opposite  to 
that  where  it  commenced,  and  with  enough  projecting 
to  reach  the  commutator,  fasten  down  the  wire  and  coat 
the  outside  of  the  coil  with  some  quick-drying  varnish. 
Remove  the  guiding  pieces  of  wood  (shown  in  Fig.  52, 
p.  47),  and  coat  the  inside  coils  with  varnish  in  a  similar 
manner.  This  will  help  to  fix  the  wire  in  its  proper 
position,  and  also  secure  better  insulation  of  one  coil 
from  its  neighbour.  The  whole  wire  should  now  receive 
one  or  two  coats  of  varnish,  the  commencing  end  of  each 
coil  being  also  painted  with  a  distinctive  colour  to 
facilitate  its  recognition  when  connecting  the  ends  to 
the  commutator  bars. 

When  the  varnish  is  dry  and  hard,  the  armature  may 
be  mounted  on  the  spindle.  The  commutator  must 
be  forced  on  tight  in  its  place,  and  fixed  close  to  the 
fibre  washer  by  screwing  up  the  nuts  on  the  threaded 
end  of  the  spindle.  It  is  well  to  have  two  nuts,  one 
to  lock  the  other  and  prevent  the  parts  from  shaking 
loose.  The  coils  may  now  be  connected  to  the  com- 
mutator bars  by  soldering  the  commencing  end  of 
one  coil  and  the  finishing  end  of  its  neighbour  to  it* 


54          DYNAMOS  AND  ELECTRIC  MOTORS. 

connector,  as  shown  at  Fig.  59.  It  will  be  found  con- 
venient to  bare  the  ends  of  the  wires  and  clean  them, 
then  to  twist  the  end  of  one  coil  round  the  commence- 
ment of  another,  so  as  to  form  a  clip  on  each  side  of  the 
connector,  and  then  to  tin  this  twisted  part  with  the 
soldering-bit  before  soldering  to  the  connector. 

When  a  small  armature  is  tightly  wound  with  a 
coil  of  fine  wire  covered  with  some  two  or  three  coats 
of  varnish,  the  whole  should  hold  well  together.  But 
there  is  always  a  danger  of  disruption,  owing  to  the 


"Fig.  59. — Connection  of  Armature  Coils  to  Commutator. 

immense  centrifugal  stress,  when  whirled  round  at  from 
2,000  to  3,000  revolutions  per  minute,  and  a  wire  thrown 
out  would  entail  disastrous  consequences  when  the 
coils  revolve  close  to  the  pole-pieces.  It  will  be  well, 
therefore,  to  bind  the  middle  of  the  armature  coils  with 
several  coils  of  tarred  tape,  so  as  to  form  a  hoop,  and 
to  wind  tightly  over  this  a  length  of  No.  24  s.w.o. 
phosphor-bronze  wire,  laid  evenly  side  by  side,  for  a 
distance  of  about  a  ^  in.  in  width.  The  ends  of  the 
wire  must  be  twisted  together  and  soldered,  using  resin 
only  as  a  flux ;  and  it  will  also  be  advisable  to  solder 


THE  GRAMME  DYNAMO.  55 

the  whole  layer  of  wires  together  here  and  there,  where 
they  pass  over  the  cogs  of  the  armature. 

The  brush-holders  and  brushes  for  this  type  of 
machine  are  not  fixed  to  the  bearings  or  to  the  pillars, 
as  is  done  in  the  small  Siemens  machine ;  they  are 
made  in  the  form  of  a  rocker,  pivoted  on  a  bridge 
attached  to  one  of  the  standards,  as  shown  at  Fig.  48 
(p.  43),  and  are  therefore  free  to  be  moved  round  the 
commutator  as  desired.  The  rocker  is  often  an  iron 
casting,  shaped  as  shown  at  Fig.  60.  The  large  hole 
in  the  centre  is  turned  to  fit  loosely  on  the  boss  of 
the  bridge  shown  at  Fig.  48.  A  hole  is  drilled  and 


c 
Fig.  60.— Rocker  for  Brush-Holder. 

tapped  in  the  crown,  as  shown  at  c,  Fig.  60,  to  receive 
a  set-screw  which  is  used  to  fix  the  rocker  in  any 
required  position.  Two  £  in.  holes,  B,  B,  are  drilled 
through  the  rocker,  these  holes  are  plugged  with  ebonite, 
and  through  each  plug  a  \  in.  hole  is  drilled  to  receive 
the  screwed  ends  of  the  brass  spindles,  s,  s,  which  carry 
the  brush  clamps,  c,  Fig.  61.  The  spindles  may  be  made 
of  |  in.  brass  rod,  and  the  outer  ends  should  come 
within  \  in.  of  the  inner  edge  of  the  commutator. 
The  inner  ends  must  be  turned  down  to  go  through 
the  ebonite  plugs  in  the  rocker,  and  screwed  to  take 
a  hexagonal  nut  on  each  side  of  the  rocker,  as  shown 
at  A,  A,  Fig.  61.  These  nuts  must  be  insulated  from 
the  rocker  by  washers  of  ebonite  or  of  vulcanised  fibre. 
The  opposite  ends  of  the  spindles  must  be  fitted  with 
two  more  hexagonal  nuts  to  hold  the  brush  clamps  ; 
these  are  of  gun  metal,  shaped  as  shown  in  Fig.  G2.  The 


56          Dm  AMOS  AND  ELECTRIC  MOTORS. 

upper  part  of  this  clamp  is  formed  to  receive  the  brushes, 
which  are  made  of  strips  of  hard  brass,  copper  gauze, 
phosphor  bronze,  or  whatever  material  may  be  chosen. 
The  strips  are  held  by  a  brass  plate  placed  on  top  of 
them,  and  secured  by  the  thumb-screw  d.  Holes  are 
bored  in  the  lower  part,  as  shown  at  e,  e,  for  the  spindle 
to  pass  through.  The  clamp  being  thus  free  to  move 
around  the  spindle,  together  with  the  movement  of  the 


Fig.  62. — Clamp  for  holding 
Brushes. 


Fig.  61.— Brush-holder 
and  Rocker  complete. 


rocker,  allows  the  brushes  to  be  adjusted  to  any  re- 
quired angle.  A  small  brass  staple  soldered  to  the 
inside  of  each  clamp  receives  the  end  of  a  spiral  spring 
threaded  on  the  spindle,  and  this  ensures  due  pressure 
of  the  brushes  on  the  commutator,  whilst  it  also  keeps 
the  clamp  in  its  proper  position  at  the  end  of  the  spindle. 
In  adjusting  the  .brushes  it  is  found  advisable  to  move 
the  rocker  by  means  of  an  insulated  handle  made  of 
ebonite  or  vulcanite,  as  shown  at  one  end  in  Fig.  61.  The 
handle  may  be  attached  by  screwing  it  on  a  short  stud 


THE   GRAMME  DVXA.MO. 


57 


fixed  in  the  end  of  the  rocker.    A  similar  handle  may  be 
fixed  at  the  other  end  if  desired. 

In  the  field  magnets  of  a  Gramme  machine  the  wire 
will  be  wound  in  four  separate  coils,  so  it  will  be  ad- 
visable to  divide  the  total  quantity  of  wire  to  be  used 
into  four  equal  parts,  and  to  treat  each  part  as  recom- 
mended in  the  case  of  the  wire  for  the  armature. 


Fig.  63.— Winding  Field  Ma^nete  of  Gramme  Dynamo. 

After  each  coil  of  wire  has  been  soaked  in  paraffin- 
wax,  it  should  be  wound  on  a  stout  wooden  bobbin, 
as  it  will  run  off  more  easily  from  a  bobbin  than 
from  a  hank.  The  method  of  winding  so  as  to  secure 
a  north  pole  piece  above  the  armature  and  a  south  pole 
piece  below  the  armature  is  shown  at  Fig.  63. 

Mount  the  core  to  be  wound  in  a  lathe  geared 
to  slow  speed.  Twist  one  end  of  the  wire  A  round  the 
core,  cross  it  over  the  pole  piece,  take  one  turn  round 


58          DYNAMOS  AND  ELECTRIC  MOTORS. 

its  own  core,  and  tie  this  turn  with  a  short  piece  of 
twine.  Then  proceed  to  wind  on  the  wire  evenly  and 
regularly,  with  the  coils  close  side  by  side,  from  the 
pole  piece  on  the  right  to  the  end  of  the  core  at  the 
left,  to  and  fro,  until  all  the  wire  has  been  wound  on  ; 
then  tie  the  last  coils  together  tightly  with  a  piece  of 
narrow  tape  to  prevent  them  from  springing  loose  when 
the  end  E  is  free.  Next  unfasten  A  from  the  right-hand 


Fig.  64. — Connecting  Fields  in  Series  and  in  Shunt. 

core,  and  commence  winding  on  the  next  coil,  beginning 
at  B  and  winding  from  left  to  right,  observing  the  same 
precautions  as  in  the  first  coil,  finishing  off  the  opposite 
end  at  H.  Next,  wind  the  cores  for  the  lower  pole  piece, 
commencing  each  at  c  and  D  respectively,  and  finishing 
off  at  F  and  i.  If  the  fields  are  to  be  connected  in 
series,  the  two  ends  E  and  F  will  now  be  led  to  the  two 
terminal  binding-screws,  and  the  two  ends  H  and  i  to 
the  two  brushes  ;  whilst  A  will  be  coupled  to  B,  and 
c  to  D  by  screw  connectors,  as  shown  by  full  lines  in 
Fig.  64.  If  the  fields  are  to  be  connected  in  shunt,  the 
two  ends  E  and  F  will  be  connected  together  to  form 


THE   GRAMME  DYNAMO. 


59 


a  continuous  coil  from  H  to  I.  These  two  ends  only  will 
be  connected  to  the  brushes,  and  from  the  brashes  two 
short  pieces  of  wire  will  go  to  each  terminal  The  dotted 
lines  in  Fig.  64  show  this  more  clearly.  When  the  two 
finishing  ends  of  the  left-hand  coils  are  connected  to  the 
two  terminals  A,  A,  and  the  two  finishing  ends  of  the  right- 
hand  coils  are  connected  to  the  brushes  B,  B,  the  circuit 
can  only  be  completed  through  the  external  circuit  in 
series  with  the  coils  and  joining  the  terminals.  But 
when  the  two  ends  of  the  left-hand  coils  are  coupled 
direct,  as  shown  at  c,  and  the  brushes  are  connected 
with  the  terminals,  as  shown  by  the  dotted  lines,  the 
current  is  shunted  through  the  coils,  and  when  the 
machine  is  running  the  cores  are  always  magnetised. 
The  cores  must  be  charged  with  initial  magnetism, 
given  by  a  battery  sending  a  current  through  the  coils, 
as  explained  on  page  38. 

The  dimensions  of  the  various  parts  have  cot  been 
mentioned  in  the  general  instructions  which  are  applic- 
able to  several  sizes  of  machines.  All  parts  are,  how- 
ever, made  proportionate  to  the  size  of  the  castings,  and 
the  vendor  of  these  will  also  supply  the  various  parts  in 
the  rough  at  a  less  cost  than  would  be  incurred  by 
making  patterns  and  having  the  parts  cast  to  order.  The 
following  list  of  Gramme  machines  gives  the  dimen- 
sions of  various  parts  and  the  output  to  be  obtained. 

TABLE  OF  GRAMME  DYNAMOS. 


££ 

ArXSfr,. 

Double  cotton 

Wire  on 
Armature, 

A'-v-,<.  p^r 
Minute. 

Power  Dneloped. 

Miil/nett. 

Diam.  Depth. 

Lbs. 

•.wo 

Ux. 

S.WO 

C.P. 

Aros. 

Vita 

UX2 

3£  X  2 

6 

22 

5 

22 

2,500 

30 

3 

40 

2X3J 

4g  X  2^ 

10 

22 

4 

20 

2,000 

65 

5 

50 

3X6 

0X6 

20 

20 

4 

16 

1,500 

150 

10 

55 

4X7 

7    X  10 

90 

16 

12 

16 

1,200 

450 

90 

55 

The  various  parts  of  the  machine  may  now  be 
assembled.  The  field  magnet  coils  should  have  two 
or  three  coats  of  varnish  to  cement  the  wire  together, 


6o 


DYNAMOS  AND  ELECTRIC  MOTORS. 


and  to  give  the  whole  a  finished  appearance.  In  ad- 
justing the  brushes,  move  the  rocker  until  by  actual 
trial  the  best  position  is  found.  This  position  is  indi- 
cated when  with  a  full  current  at  the  terminals  there  is 
very  little  noise  at  the  brushes,  and  little  or  no  sparking 
where  the  brushes  touch  the  bars  of  the  commutator. 

Machine  No.  1  has  a  solid  cogged  armature ;  all  the 
others  are  built  up  of  cogged  laminated  plates.  The 
armature  of  No.  4  has  two  strands  of  No.  16,  used 
side  by  side  to  carry  the  current  in  the  armature  coils. 

The  following  table  will  help  in  determining  the 
horse-power  needed  to  drive  Gramme  dynamos  : — 


ATos. 

Watts. 

C.P. 

H.P.  Required. 

1 

120 

30 

I  to  I 

2 

250 

65 

ito£ 

3 

550 

140 

1 

4 

1,650 

430 

2* 

CHAPTER  IV. 

THE  MANCHESTER  DYNAMO. 

THE  Manchester  dynamo  shown  at  Fig.  65  (introduced  by 
Messrs.   Mather    and    Platt,    of    Salford,   Manchester) 


Fig.  63. — Manchester  Dynamo  complete. 

now  claims  our  attention.  In  point  of  simplicity  in 
construction  and  in  usefulness  it  is  superior  to  the 
Siemens  and  Gramme  machines  already  described. 


63          DYNAMOS  AND  ELECTRIC  MOTORS. 

The  carcase  of  a  Manchester  dynamo  may  be 
made  up  from  four  castings.  These  consist  of  the  bed- 
plate and  bottom  pole  piece  in  one  casting,  and  the 
top  pole  piece  and  yoke  also  in  one  casting,  and  the  two 
cores.  The  whole  arrangement  is  shown  in  section  at 
Fig.  G6,  where  A  represents  the  top  pole  piece.  B 
the  lower  pole  piece,  and  c,  c,  the  two  cores.  From 
this  illustration  it  will  be  seen  that  the  two  cores  form 
pillars  to  support  the  upper  pole  piece  and  yoke. 
The  cores  should  have  threaded  pins  of  wrought-iron 


Fig.  66. — Section  of  Manchester  Dynamo,  showing 
winding  of  Field  Magnet  Cores. 

cast  in  each  end.  These  pins  pass  through  holes  drilled 
in  the  top  yoke  and  the  bottom  bed-plate,  and  the  cores 
are  securely  fastened  to  those  parts  by  nuts  fitted  to  the 
screwed  pins. 

The  cores  and  pole  pieces  of  all  dynamos  should  be 
made  of  the  best  soft  iron,  the  cores  being  fitted  with 
flanges.  These  flange  ends,  together  with  a  corresponding 
round  area  on  the  yoke  and  bed-plate,  should  be  turned 
bright  and  fitted  close  together.  This  is  done  before 
the  cores  are  wound  with  wire,  so  it  will  be  much  easier 
to  wind  them  thus  made  up  in  the  form  of  bobbins ;  the 
wire  will  be  protected  from  injury  whilst  bolting  the 
parts  of  the  machine  together,  and  tne  magnetic  con- 
nection between  the  cores  and  pole  pieces  will  be 
good. 


THE  MANCHESTER  DYNAMO.  63 

When  .cores  are  not  thus  flanged]  it  frequently 
happens  that  whilst  bolting  the  parts  together  the  iron 
of  the  upper  pole  piece  or  yoke  is  forced  into  electric 
connection  with  some  of  the  coils  of  wire,  and  this  alone 
is  the  cause  of  some  failures  with  this  class  of  machine. 
The  difference  in  magnetic  intensity  of  the  field  is  often 
most  marked  when  cores  are  thus  carefully  brought  into 
cloae  connection  with  the  pole  pieces.  As  the  efficiency 
of  the  machine  depends  largely  upon  its  field  magnets, 
this  point  should  not  be  neglected.  : 

Figs.  67,  68,  and  69  show  how  the  flanges  may  be 
put  on ;  Fig.  67  shows  the  core  as  in  general  use ;  and 
Fig.  68  the  same  core  with  a  light  fillet  cut  in  a  lathe, 


Fig.  67.  Fig.  68.  Fig.  69. 

Fig.  67. — Magnet  Core  for  Manchester  Dynamo. 

Fig.  68.— Core  with  Fillets  to  receive  Flanges. 

Fig.  69.— Core  Fitted  with  Iron  Flanges. 

on  each  end.  This  core  must  fit  the  hole  in  a  wrought- 
iron  collar  or  washer  when  the  collar  is  hot,  and  when 
cold  the  collar  will  be  firmly  fixed.  Fig.  69  shows  the 
collars  shrunk  on  the  core  and  turned  up  bright.  The 
field  magnet  cores  may  be  wound  with  wire  in  the  same 
manner  as  those  of  the  Gramme  machine  ;  that  is,  so  as 
to  make  the  top  a  north  pole  and  the  bottom  a  south 
pole,  as  described  in  Chapter  III.,  where  the  method  of 
connecting  the  ends  is  also  given. 

The  ring  or  the  H-girder  forms  of  either  solid  or 
laminated  armatures  may  be  easily  adapted  to  the  Man- 
chester field.  In  some  of  these  machines  Pacinotti  cogged 
armatures  are  employed ;  in  some  others  the  Gramme 
ring.  For  small  armatures  the  H  form  is  convenient,  and 
will  be  most  efficient  when  built  up  of  laminated  plates,  as 
shown  at  Fig.  10  (p.  16).  When  armatures  of  the  Gramme 
or  Pacinotti  type  are  used,  it  will  be  necessary  to  build 


64 


DYNAMOS  AND  ELECTRIC  MOTORS. 


up  the  commutator  as  described  in  the  last  chapter  for  a 
Gramme  machine,  because  we  must  have  a  commutator 
with  several  sections  to  receive  the  ends  of  the  armature 
coils.  But  when  the  H -girder  form  of  armature  is 
chosen,  we  must  also  select  the  two-part  commutator 
used  in  the  Siemens  machine,  and  illustrated  at  Figs. 
33,  34,  35  (pages  29  and  30). 

The  massive  and  broad  cast-iron  bed-plate  carries 
the  bearings  on  each  side  of  the  pole  pieces,  and  these 
are  set  wide  enough  apart  to  admit  a  long  armature 
spindle.  We  have  therefore  room  enough  for  a  rocker 
arrangement  and  adjustable  brush-holders  such  as  those 
shown  at  Figs.  GO,  61,  62  (pages  55  and  5G).  The  rocker 
works  on  a  gun-metal  sleeve  fixed  to  the  inside  of  one 
of  the  brackets.  The  brushes  are  best  made  of  copper 
wire  gauze  soldered  to  thin  strips  of  sheet  copper.  Con- 
nections between  them  and  the  wires  should  be  made 
as  directed  for  the  Gramme  machine. 

The  instructions  for  winding  the  armature  and  all 
other  necessary  particulars  in  the  chapters  on  the 
Siemens  and  Gramme  machines  apply  equally  to 
a  machine  with  field  magnets  of  the  Manchester  type, 
and,  indeed,  to  all  others. 

The  following  table  gives  particulars  of  Manchestei 
dynamos  of  various  sizes. 

LIST  OF  MANCHESTER  TYPE  DYNAMOS. 


Size 
of  Cores. 
Inches. 

Armature. 
Inches. 

Wire  on 
F.M.'s. 

Wire  on 
Armature. 

Output  obtainable. 

Revs,    j 
per     j 
Min.    ; 

Diam.Lgtb 

Diara.Lgth. 

Lbs. 

s.w.o. 

Lbs. 

s.w.a. 

Volts. 

Amps. 

C.P. 

i£x  4 

3iX  2 

6 

22 

U 

22 

40 

3 

30 

2.5001 

2*  X  6|- 

4iX2£ 

10 

22 

4 

20 

50 

5 

65 

2,000- 

3    X7i 

6X6 

20 

20 

4 

16 

50 

10 

125 

1,500' 

4    X  10 

7X7 

90 

16 

12 

16 

50 

30 

400 

1,200- 

All    the    above    machines    are    intended    to    have* 
laminated  cogged  ring   armatures.     That  the  last   i* 


THE  MANCHESTER  DYNAMO.  65 

to  be  wound  with  two  strands  of  No.  16  wire  run  side 
by  side,  and  wound  on  together.  This  is  found  more 
convenient  for  winding  than  a  coarser  wire,  and  the 
effects  obtained  are  equally  good.  After  winding  on  two 
strands  in  this  way,  the  ends  should  be  bared,  twisted 
together,  and  soldered,  before  fastening  them  to  the 
commutator  bars.  Large  machines  are  furnished  with 
Gramme  armatures,  often  wound  with  forty  or  more  coils 
of  wire.  The  small  machines  have  fewer  coils  on 
their  armatures.  Some  large  machines  have  also 
compound  wound  field  magnets — that  is,  the  cores  are 
wound  with  two  sizes  of  wire,  the  smaller  connected 
in  shunt  with  the  armature,  the  larger  being  in  series 
with  the  armature  winding  and  outer  circuit.  In  the 
small  machines  above  described,  the  field  magnet  coils 
should  be  connected  in  shunt  with  the  armature.  In 
making  arrangements  for  connecting  the  machine  with 
the  outer  circuit,  it  will  be  advisable  to  mount  a  slab 
of  polished  mahogany  or  other  hard  wood  on  the  top  of 
the  dynamo,  as  shown  in  section  at  D,  Fig.  66,  and  screw 
the  terminals  into  the  wooden  slab  as  shown. 


66 


CHAPTER  V. 

THE  SIMPLEX  DYNAMO. 

Tui3  chapter  will  describe  the  construction  of  a  small 
dynamo,  or  motor,  made  almost  entirely  of  wrought- 
iron  forgings,  which  can  be  obtained  from  any  smith  or 
made  by  the  dynamo  maker  himself. 

This  machine  generates  a  current  of  5  amperes  at  a 
pressure  of  10  volts;  and  is  about  capable  of  lighting 
two  8  candle-power  lamps  when  used  as  a  dynamo, 
and,  being  shunt-wound,  is  also  suitable  for  charging 
storage  batteries.  When  used  as  a  motor,  running  at 
about  2,500  revolutions  per  minute,  its  power  will  be 
about  1*5  h.-p.  The  current  required  will  be  about 
5  amperes  at  15  volts. 

To  drive  this  machine  about  i  horse-power  would 
be  required.  An  engine  to  develop  this  horse-power 
would  have  the  following  dimensions  :— Cylinder,  2  in. 
bore,  2  in.  stroke ;  revolutions  of  fly  wheel,  200  per 
minute ;  boiler  about  18  in.  by  9  in. ;  pressure,  20  Ibs. 
on  square  inch. 

The  armature  is  of  the  old  Gramme  ring  type, 
constructed  of  soft  iron  wires  over-wound  with 
insulated  copper  wires.  About  l£  Ib.  of  No.  20  to 
24  S.W.G.  iron  wire  will  be  required,  and  also  a  circular 
wooden  mandrel,  or  former,  of  shape  and  dimensions 
shown  in  Fig.  70.  This  former  should  be  turned  from 
hard  wood,  with  one  of  the  flanges  or  cheeks  removable, 
so  that  the  iron  ring  when  completed  may  be  slipped 
off ;  for  the  same  purpose  the  former  should  be  covered 
with  a  layer  of  smooth  paper,  the  edges  of  which 
may  be  held  in  place  with  sealing-wax.  To  wind 
on  the  iron  wire,  the  former  should  either  be  mounted 
between  the  centres  of  a  lathe,  or  a  pin  should  be  driven 


THE  SIMPLEX  DYNAMO.  67 

into  the  centre  of  each  end,  and  the  former  mounted 
between  two  wooden  supports,  as  shown  in  Fig.  70. 
The  wire  should  be  wound  upon  the  former  in  even 
layers,  with  a  coat  of  shellac  varnish  between  every  two 
layers,  until  the  outside  diameter  of  the  ring  is  2|  in.; 
the  thickness  of  the  core  will  then  be  about  f  in. 
The  whole  surface  of  the  armature  should  be  coated 
with  shellac  varnish,  and  the  armature  and  former 
placed  in  a  hot  oven  until  the  shellac  melts  and  binds 
the  iron  wires  together.  When  cool,  the  removable 
cheek  may  be  unscrewed,  and  the  armature  should 
then  slip  off  the  former  easily.  The  armature  should 
then  be  insulated  by  entirely  covering  it  with  silk  tape, 


Fig.  70. — Mandrel   or   Former  for  making  Core  of  Arma- 
ture of  Simplex  Dynamo. 

the  edges  of  which  must  overlap,  and  the  surface  then 
coated  with  shellac  varnish.  When  dry,  the  winding  of 
the  armature  may  be  proceeded  with.  It  is  not  essential 
for  the  iron  wire  of  the  armature  coil  to  be  in  one 
continuous  hank  or  coil ;  the  core  may  be  built  up  of  a 
number  of  hanks,  provided  that  the  length  of  wire  con- 
tained in  each  is  considerable,  and  that  each  added 
piece  is  properly  joined  to  the  wire  last  wound.  To 
join  the  wires,  twist  the  ends  together,  coil  the  joint 
upon  the  layers  of  wire  previously  wound,  and  coat 
with  shellac  varnish.  When  this  is  hard,  file  the  joint 
down  level  with  a  smooth  file,  again  varnish,  and  pro- 
ceed with  the  winding. 

The  armature  is  completely  overwound  with  three 
layers  of  No.  20  s.w.o.  double  cotton-covered  copper 
wire  divided  into  twenty  sections  or  coils,  each  section 


68          DYNAMOS  AND  ELECTRIC  MOTORS. 

having  twenty-four  turns  of  wire,  the  whole  weigh- 
ing about  f  Ib.  Before  proceeding  to  wind  on  the 
wire,  the  armature  should  be  firmly  fixed  to  a  bench 
or  table  by  passing  a  strip  of  hard  wood  through  the 
interior  and  fastening  the  strip  to  the  bench  by  screw- 
ing in  the  manner  shown  in  Fig.  71.  For  the  purpose 


Fig.  71. — Clamp  for  Armature  Core. 

of  facilitating  the  winding  and  also  to  keep  the  arma- 
ture properly  balanced,  it  is  best  to  divide  the 
armature  with  a  pair  of  compasses  into  a  number  ot 
equal  parts,  and  to  treat  each  part  separately.  Thus,  if 
the  armature  is  divided  into  four  parts,  five  sections 
will  be  allotted  to  each  part,  and  the  coils  can  be 
arranged  so  as  to  fill  the  spaces  allotted  to  them.  A 
sufficient  length  of  wire  to  reach  twenty-four  times 
around  the  armature,  with  about  one  foot  over  for  con- 
nections, etc.,  having  been  cut  off,  one  end  is  fastened  to 
the  hardwood  strip,  as  shown  in  Fig.  71,  and  the  wire  is 


Fig.  72. — Method  of  winding  Ring  Armature. 

then  carried  over  the  top  of  the  armature  and  threaded 
through  the  inside,  and  pulled  tight.  This  is  repeated 
three  times ;  the  last  inside  turn  rests  upon  the  two 
wires  previously  wound,  as  represented  at  A,  Fig.  72.  The 


THE  SIMPLEX  DYKAMO.  69 

wire  is  thus  wound  alternately  upon  the  interior  surface 
of  the  armature  and  upon  the  preceding  turns  until 
eight  turns  have  been  completed,  when  the  wire  is  tem- 
porarily fastened  to  the  hardwood  strip  until  the  next 
layer  is  commenced. 

The  second  section  is  commenced  and  ended  in 
the  same  way,  and  the  winding  proceeds  thus  until 
about  five  or  six  sections  have  been  wound  upon  the 
armature.  The  outside  wire  should  be  beaten  down  flat 
with  a  small  wooden  mallet,  and  the  wires  on  the  inside 
surface  should  be  pressed  with  a  wooden  rod  for  the 
same  purpose.  A  coat  of  shellac  varnish  should  then 
be  applied  to  the  wires,  and  when  this  becomes  hard 
the  second  layer  is  proceeded  with  in  exactly  the 
same  way  as  the  first  layer,  with  the  exception  that 


Fig.  73.— Wooden  Plug  for  Armature. 

the  wires  on  the  inner  surface  of  the  armature  are 
arranged  between  those  already  wound,  as  repre- 
sented in  Fig.  72,  where  the  white  circles  show  the 
first  layer,  and  the  black  circles  the  second  layer. 
When  this  second  layer  is  completed,  the  first  layer 
on  the  second  portion  of  the  armature  may  be  com- 
menced, and  when  two  layers  have  been  wound  upon 
half  of  the  armature,  the  third  layer  may  be  wound 
on  in  exactly  the  same  way  as  the  first  layer. 

After  this  third  layer  is  completed,  the  ends  of  the 
sections  may  be  permanently  coupled  up  by  cleaning, 
twisting,  and  soldering  the  adjacent  ends  of  the  sec- 
tions together,  the  finishing  end  of  one  section  being 
connected  to  the  commencing  end  of  the  next  section,  as 
shown  at  B,  Fig.  72.  The  whole  armature  should  then 
be  coated  with  shellac  varnish.  A  hardwood  plug 


•jo          DYNAMOS  AND  ELECTRIC  MOTORS. 

(Fig.  73)  is  next  made,  through  this  a  spindle  of  \  in. 
steel  is  driven  tight,  and  the  plug  is  then  driven  tight 
into  the  armature.  The  armature  should  now  revolve 
truly  upon  the  spindle,  and  to  prevent  the  wires  from 
bulging  out  when  the  armature  is  revolving  use  binding- 
wires  consisting  of  two  bands  each  of  twelve  strands 
of  No.  36  S.W.G.  copper  or  brass  wire  wound  upon  two 
£-in.  strips  of  thin  mica  or  paper  and  soldered  together 
so  as  to  form  solid  bands.  When  these  are  completed 
the  armature  may  be  connected  to  the  commutator. 

The  commutator  consists  of  a  brass  washer,  2  in.  is 
diam.  and  about  %  in.  thick,  with  twenty  countersunk 
holes  drilled  at  equal  distances  apart,  and  fastened 
against  a  hardwood  disc  with  twenty  brass  screws  |  ia 


Fig.  74. — Commutator  of  Simplex  Dynamo. 

long,  as  shown  in  Fig.  74.  A  hole  should  be  drilled 
through  this  disc  to  fit  tight  on  the  shaft.  After 
being  screwed  to  the  disc  the  washer  is  sawn  into 
twenty  segments,  which,  being  divided,  are  insulated 
from  each  other  though  fastened  to  the  hardwood 
disc.  Each  of  the  twenty  separate  armature  sections 
is  composed  of  twenty-four  turns  in  three  layers, 
each  having  one  commencing  end  and  one  finishing  end 
— so  there  will  be  a  total  of  forty  ends  in  the  whole 
armature.  These  are  cleaned,  and  the  commencing 
end  of  each  coil  is  twisted  to  the  finishing  end  of  the 
adjacent  coil  all  round  the  armature.  The  separate 
windings  will  thus  form  a  continuous  spiral,  and  twenty 
ends  will  be  left.  These  ends  are  soldered  one  to  each 
of  the  twenty  brass  screws  holding  the  commutator 
segments.  The  ends  of  the  wires  are  soldered  to  the 
ends  of  the  screws,  which  project  through  the  disc 
as  shown  in  Fig.  74.  The  disc  should  then  be  driven 


THE  SIMPLEX  DYNAMO.  71 

over  the  spindle  and  screwed  to  the  centre  plug.  A 
layer  of  string  over  the  screws  completes  the  arma- 
ture, which  is  thus  represented  in  Fig.  75. 

The  field  magnet  is  of  wrought  iron,  of  shape  and 
dimensions  shown,  and  consists  of  the  two  pole  pieces 
(Fig.  76)  and  the  yoke  (Fig.  77).  Two  coil  flanges  will 
also  be  required.  The  two  pole  pieces  are  fitted  so 
that  the  armature  revolves  in  the  space  between 
with  a  clearance  of  about  -^  in.  They  are  fixed  to 
the  yoke  by  means  of  two  -^  in.  screws  or  rivets.  The 
coil  flanges  are  of  hard  wood,  zinc,  or  sheet  brass,  and 
are  slipped  over  the  magnet  core  and  held  in  place  by 
the  wire.  Before  fixing  the  pole  pieces,  the  magnet 
should  be  wound  with  about  3  Ibs.  of  No.  22  s.w.o. 


Fig.  75.— Armature  of  Simplex  Dynamo  complete. 

single  cotton-covered  copper  wire.  The  yoke  is  first 
covered  with  a  layer  of  paper,  and  the  wire  is  then 
wound  upon  it  in  even  layers,  until  the  entire  space  is 
filled,  when  a  coat  of  shellac  varnish  is  applied  to  the 
wire,  and  the  pole  pieces  and  bed-plate  are  fixed  per- 
manently to  the  magnet  by  suitable  screws. 

Cast  iron  may  be  used  for  the  field  magnet,  but  as 
it  has  a  lower  permeability  than  wrought  iron  the 
sectional  area  must  be  increased.  Therefore  make  the 
cast-iron  field  magnet  1 J  in.  instead  of  |  in.  in  thickness. 
Wire  of  the  same  thickness  (22  s.w.o.)  may  be  used  as 
with  thewrought-iron  core,  but  more  of  it  will  be  required. 

The  bed-plate  is  also  of  wrought  iron,  and  is  shown 
in  Fig.  79.  Through  it  are  drilled  three  -^  in.  counter- 
sunk holes  for  wood  screws,  four  -^  in.  tapped  holes  for 
holding  down  the  bearings,  and  three  ^  in.  clearance 


72          DYNAMOS  AND  ELECTRIC  MOTORS. 

holes  for  fixing  the  bed-plate  to  the  magnet.  The  bed- 
plate is  fixed  to  the  yoke  by  means  of  two  Ts¥  in.  screws 
or  rivets,  which  also  fix  the  lower  pole  piece,  and  by 


Fig.  76.— Pole  Piece  of  Simplex  Dynamo. 

a  third  screw  underneath  the  yoke,  as  shown  in  Fig.  77. 
The  bearings  (Fig.  80)  are  made  of  brass,  and  each 


Fig.  77.— Simplex  Dynamo  Yoke  for  Magnet. 

consists  of  an  upright  piece  drilled  with  a  \  in.  hole  to 
carry   the    armature    and    spindle,    and   a    base-plate 


Fig.  78.— Coil  Flange. 

soldered  to  the  upright  piece  and  fixed  to  the  bed- 
plate by  two  fV  in.  screws.  One  of  the  bearings  is  also 
drilled  with  a  small  hole  in  the  upright  piece  fof 
fixing  the  brush-holder,  as  shown  in  Fig.  80. 


THE  SIMPLEX  DYNAMO. 


73 


The  brush-holder  (Fig.  81)  is  made  of  sheet  brass, 
«bout  \  in.  thick,  drilled  with  a  i-in.  hole  in  centre,  and 
two  holes  at  each  end  to  take  wood  screws,  which  secure 


Fig.  79.— Bud-Plate  of  Simplex  Dynamo. 

small  pieces  of  ebonite  or  boxwood.  These  serve  to  insu- 
late and  carry  the  brushes,  which  are  made  of  thin  sheet 
brass  or  copper  at  one  end  drilled  with  two  small  holes, 
for  taking  round-headed  brass  screws,  one  of  which 
fixes  the  brush  to  the  insulating  block  while  the  othei 


Fig,  80.— Bearings  of  Armature. 

fixes  to  the  brush  the  flexible  connecting  wire  from  the 
terminal.  The  screws  holding  the  brushes  must  not 
be  in  metallic  contact  with  the  brush-holder  itself. 
A  small  slot  is  also  made  as  shown  in  the  brush- 
holders,  so  that  the  brushes  may  be  moved  through  a 
small  arc  until  the  correct  position  is  found  on  the 
commutator.  Then  the  brush-holder  is  fixed  by  a  small 
screw,  as  shown  in  Fig.  82,  which  represents  the  com- 
plete machine. 

The  terminals  can  be  of  almost  any  of  the  well-known 
types,  as  Figs.  14  to  20  (pp.  18  to  20),  and  may  either  be 


74          DYNAMOS  AND  ELECTRIC  MOTORS. 

fixed  upon  a  hardwood  board  placed  upon  the  magnets, 
as  shown  in  Fig.  82,  or  upon  a  board  carrying  the  whole 
machine.  In  either  case  the  wires  from  the  magnet, 
coil,  and  brushes  are  connected,  as  shown  in  Fig.  82. 


Fig.  81.— Brush-Holder. 

The  pulley  may  be  of  brass,  from  \\  in.  to  2  in.  in 
diameter,  about  1  in.  on  the  face,  and  fixed  to  the 
spindle  either  by  a  screw  or  a  key.  The  belt  should  be 
of  leather,  about  1  in.  in  width,  and  not  more  than  \  in. 


Fig.  82. — Simplex  Dynamo  complete. 

thick.      The  machine  may  be  finished  by  giving  it  a 
coat  of  paint  and  then  varnishing. 

To  start  the  dynamo,  run  the  armature  at  from 
2,500  to  3,000  revolutions  per  minute,  and  if  the  machine 
is  properly  constructed  it  will  excite  itself  after  the 
fields  have  been  initially  magnetised  by  the  current 


THE  SIMPLEX  DYNAMO.  75 

from  a  small  battery.  If  the  machine  is  wanted  to 
run  as  a  motor,  about  seven  or  eight  chromic  acid  cells 
or  accumulator  cells  will  be  required.  It  is  immaterial 
which  is  the  north  or  south  pole  of  the  magnet.  The 
commencing  end  of  the  field-magnet  coil  must  be  con- 
nected to  one  brush,  and  its  finishing  end  to  the  other 
brush. 

Below  are  given  dimensions  of  a  shunt-wound 
dynamo  for  lighting  four  10-candle-power  lamps,  at  a 
pressure  of  15  volts,  this  being  also  suitable  for  charging 
six  accumulator  cells  if  the  latter  are  required.  The 
current  will  be  10  amperes,  and  the  speed  2,500  revolu- 
tions per  minute.  Armature,  2£  in.  wide,  3  in.  diameter, 
core  |  in.  thick,  constructed  of  annealed  iron  wires,  and 
wound  with  two  layers  of  No.  16  B.W.G.  double  cotton- 
covered  copper  wire,  divided  into  twenty  sections, 
each  in  two  layers,  with  eight  turns  per  layer— total 
turns  of  wire  on  armature,  320.  Diameter  of  spindle, 
|  in.  ;  outside  diameter  of  commutator  disc,  3  in. ; 
inside  diameter,  If  in. ;  thickness  of  segments,  £  in. 
Field  magnet  of  rectangular  wrought  iron  2|  in.  wide  by 
\\  in.  thick.  Length  of  field  coil,  4£  in. ;  thickness  of 
pole  piece,  about  \  in.  Flanges  of  bobbin,  about  \  in. 
thick.  Bobbin  wound  with  about  11  Ib.  No.  18  S.W.G. 
single  cotton-covered  copper  wire.  With  an  engine 
running  at  300  revolutions  per  min.,  and  a  flywheel  of 
18  in.  diameter,  a  pulley  about  2i  in.  diameter  by  \\  in. 
wide  would  be  required  on  the  armature  spindle  to  get 
2,500  revolutions. 


CHAPTER    VI. 

CALCULATING    THE    SIZE    AND    AMOUNT    OF     M IEB    FOB 
SMALL  DYNAMOS. 

WE  commence  with  the  armature,  because  all  other 
parts  are  subordinated  to  it.  When  a  loop  of  copper 
wire  is  placed  between  the  poles  of  a  magnet  in  such 
a  manner  as  to  vary  the  lines  of  magnetism  supposed 
to  be  passing  through  it,  an  electro-motive  force  is  set 
up  in  the  loop.  This  principle  governs  all  dynamo- 
electric  machines.  The  loop  of  wire,  multiplied  many 
times  and  wound  over  a  core  of  iron,  is  named  the 
armature,  and  the  magnet  corresponds  to  the  field  of 
the  machine. 

Amongst  other  things,  the  length  of  wire  on  the 
armature  determines  the  voltage  ;  and  in  small  machines 
the  safe  carrying  capacity  of  this  wire  determines  the 
current  obtainable.  The  size  and  form  of  an  armature 
are  determined  by  the  desired  output  of  the  machine. 
'  .  The  armatures  most  in  use  may  be  classed  under 
one  of  three  types — viz.,  the  shuttle,  the  ring,  and  the 
drum.  These  three  types  admit  of  several  variations. 
In  the  shuttle  type,  one  coil  of  wire  is  wound  in  the 
channel  between  the  two  cheeks,  and  the  two  ends  of 
the  coil  are  attached  to  two  halves  of  a  commutator  ring. 
In  the  ring  type,  some  six,  eight,  or  more  wire  coils  each 
of  the  same  length  are  wound  in  sections  over  the  ring, 
the  ends  of  each  coil  being  brought  out  and  soldered  to 
as  many  bars  on  the  commutator  as  there  are  coils  on 
the  armature,  the  finishing  end  of  one  coil  and  the 
commencing  end  of  the  next  being  soldered  to  one  bar. 
In  the  drum  type  the  coils  of  wire  are  wound  in  sections 
altogether  over  the  armature,  not  through  the  ring,  as 
in  the  ring  form,  but  the  coils  we  connected  in  the 
same  manner. 


CALCULATING   WIRE  FOR  SMALL  DYNAMOS.  77 

The  shuttle  form  of  armature  is  most  easily  wound 
and  connected,  but  its  use  is  confined  to  small  machines. 
This  specially  applies  to  solid  shuttle  armatures,  as 
these  soon  get  so  hot  as  to  reduce  the  output  of  the 
machine  and  endanger  the  insulation  of  the  wire. 
When  the  shuttle  is  laminated — that  is,  built  up  of  thin 
iron  plates — this  tendency  is  considerably  modified.  It 
is  the  type  of  armature  usually  employed  in  model 
dynamos,  with  fields  of  the  simple  horseshoe  or  Siemens 
type  (See  Chap.  II.). 

The  ring-type  of  armature  is  preferable  to  the 
shuttle  for  larger  dynamos,  but  is  very  difficult  to 
wind  when  small,  since  the  space  through  which  to 
pass  the  spool  carrying  the  wire  becomes  more  and 
more  contracted  with  each  layer  and  section  of  wire 
wound.  It  is  generally  used  in  dynamos  with  fields  of 
the  Gramme,  Manchester,  Brush,  Kapp,  and  Simplex 
types. 

The  drum  type  of  armature  is  more  easily  wound 
than  the  ring,  since  all  the  wire  is  wound  over  the  arma- 
ture outside  in  sections  ;  but  it  is  difficult  to  connect,  as 
the  winder  is  apt  to  lose  sight  of  the  exact  order  in 
which  the  ends  of  wire  are  to  be  connected.  If  each 
coil  is  marked  with  a  different  tint  or  colour  of  cotton  or 
silk  thread,  this  trouble  will  be  much  mitigated. 

The  voltage  obtainable  from  a  shuttle  dynamo  is 
roughly  determined  by  the  length  of  insulated  copper 
wire  coiled  on  its  armature.  The  diameter  of  the  wire 
governs  the  length  that  can  be  got  on  an  armature  of 
a  given  size.  In  model  dynamos,  each  yard  of  active 
wire  on  the  armature  will  give  about  1  volt  (all 
other  conditions  being  favourable)  when  moving  at  a 
circumferential  velocity  of  1,250  ft.  per  minute.  This 
last  statement  requires  some  explanation  to  make  it 
clear.  Active  wire  is  that  portion  of  each  coil  of 
wire  which  is  employed  in  cutting  through  the  lines 
of  magnetic  force  given  out  by  the  field-magnets.  On 
a  drum  armature,  all  the  wire  except  the  parts  of  the 
coils  over  the  ends  of  the  drum  is  active  wire.  The 


DYNAMOS  AND  ELECTRIC  MOTORS. 


dead  wire  on  a  drum  or  a  shuttle  armature  should  not 
exceed  one-third  of  the  total  length  employed ;  but 
for  this  efficiency  the  length  of  the  armature  must  not 
be  less  than  three  times  its  diameter.  In  a  ring  arma- 
ture, the  relative  quantities  of  dead  and  active  wire 
will  depend  upon  the  thickness  of  the  ring. 

The  circumferential  velocity  of  the  wire  coils  may 
be  taken  to  be  the  same  as  that  of  the  periphery  of 
the  armature  on  which  they  are  wound.  As  the 
circumference  of  a  ring  or  drum  is  3'14  times  its 
diameter,  multiply  the  diameter  of  the  armature  in 
inches  by  314  to  ascertain  its  circumference  in  inches. 
This  done,  find  how  many  times  it  will  have  to  turn  to 
cover  a  foot  length,  and  multiply  this  number  by  1,250 
to  find  how  many  revolutions  the  armature  must  make 
in  a  minute  to  produce  one  volt  from  each  active  yard 
of  wire  in  its  coils.  It  will  thus  be  seen  that  the 
voltage  is  conditional  on  the  speed  of  the  armature  ;  it 
is  also  conditional  upon  the  strength  of  the  magnetic 
rield,  which  must  be  at  its  maximum  to  get  the  best 
result.  The  following  table  gives  particulars  of  the 
weight,  resistance,  carrying  capacity,  etc.,  of  copper 
wire  in  sizes  on  the  Birmingham  Wire  Gauge. 

PROPERTIES  OF  B.W.G.  COPPER  WIRES. 


* 

r 

8  fe 

I 

Is 

K 

4 

|| 

Approximate 
Yards  to  Ib. 

|| 

«  6, 
§| 

I 

II 

* 

*H 

** 

6> 

!* 

fj 

8 

•165 

Bare 

4-05 

Silk 

4 

Cotton'.Sllk 

4    \    5 

CuU'. 

5 

•00475 

2564-1 

40 

10 

•134 

6-14 

6 

5'8    7 

6 

•0109 

1666-6 

28 

12 

•109 

9-28 

9 

8'8    9 

8 

•0249 

1098-9 

18 

14 

•083 

16 

157 

15-5 

11 

10 

•0741 

666-6 

10 

16 

•065 

26 

25'5 

24 

14 

13 

•1971 

400 

6 

18 

•049 

47-9 

47 

45 

19 

16 

•6629 

2127 

3 

20 

•035 

85 

83 

80 

25 

23 

2-095 

120-4 

2 

22 

•028    131 

129 

120 

29 

27 

4-976 

77'5 

1-5 

24 

•022  1  176-4 

173 

162 

34 

30 

9-009 

57-8 

1 

CALCULATING   WIRE  FOR  SMALL  DYNAMOS.  70 


Carrying  capacity  in  amperes  is  calculated  at  about 
2,000  amperes  per  square  inch.  The  safe  carrying 
capacity  of  the  wire  is  the  maximum  current  it  will 
carry  without  heating  to  such  an  extent  as  to  affect 
the  insulation  seriously.  In  a  series  shuttle  dynamo, 
the  current  in  the  outer  circuit  passes-  through  armature 
coils  and  field-magnet  coils ;  therefore  the  wire  on  the 
latter  should  be  of  a  diameter  about  equal  to  that  on 
the  former.  The  accompanying  tables  will  serve  as  a 
guide  to  selecting  suitable  wire  'for  the  armature  and 
field-magnet  coils.  The  following  table  deals  with 
wires  on  the  Standard  Wire  Gauge. 

PROPERTIES  OF  S.W.Q.  COPPER  WIRES. 


WEIGHT 

RESISTANCE 

No.  OF  TURNS 

CURRENT  IN 

IN  LB. 

IN  OHMS. 

PER  INCH. 

AMPERES. 

tl 

4 

^ 

ft 

11 

If 

It 
tt 

|l 

si 

» 

| 

I 

1 

it 

|s 

{? 
i.i 

& 

I1 

CO  $i 

1 

1 

£ 

I 

A 

B 

C 

51 

51 

ft 

22 

•028 

•0006 

7 

12 

4078 

71-8 

24 

28 

26 

•6 

•9 

T2 

20 

•036 

•ooio 

12 

21 

24'11 

43-4 

20 

2G 

23 

1 

1*5 

2 

19 

18 

'040 
'048 

•0012 
•0018 

15 
21 

26 

37 

19-9835-2 
13'88  24'4 

18 
16 

23 

20 

20 
17 

1-2 
1-8 

1-8 
27 

2'4 
3-6 

17 

•056 

•0024 

28 

50 

10-2 

17'9 

14 

17 

15 

2'4 

3'6 

4'8 

1G 

•064 

•0032 

37 

66 

7'6 

13-6 

12-8 

15 

14 

3'2 

4'8 

6'4 

15 

•072 

•0040 

47 

83 

6-11 

10-7 

11-5 

13 

12 

4 

6 

8 

14 

'080 

•0050 

57 

102 

5' 

8'8 

10-5 

11 

10 

5 

7'5 

10 

13 

•092 

•0066 

76 

135 

378 

6-6 

9'5 

10 

9 

6'6 

9'9 

13-2 

12 

•104 

•0085 

98 

173 

2-95 

5-2 

8-5 

9 

8 

8'5 

1275 

17 

11 

•116 

•0105 

122  215 

2-36 

4'2 

7-5 

7 

6 

10-5 

1575 

21 

10 

•128 

•0128 

148  262 

1'95 

3'4 

7 

6 

8 

12-8 

19-2 

25'6 

9 

•144 

•0162 

188  332 

1'55 

27 

6 

5 

5 

16'2 

24'3 

32-4 

8 

•160 

•0201 

245  409 

1-26 

2'2 

57 

4 

4 

20'1 

30'15 

40-2 

The  resistances  given  above  are  for  100  per  cent 
conductivity  copper  at  a  temperature  of  about  65°  F. 


8o          DYNAMOS  AND  ELECTRIC  MOTORS. 

Under  the  heading  "No.  of  turns  per  inch"  will  be  seen 
three  divisions— A,  B,  and  c.  Of  these  B  and  c  refer 
to  wires  which,  in  the  small  sizes,  have  special  thin 
coverings  of  silk  and  cotton  respectively.  Under  A  the 
insulation  is  reckoned  at  the  rate  of  12  mils  =  ^TQ  ^n-  °^ 
double  cotton  in  sizes  below  No.  16.  Above  this  size 
the  average  covering  is  about  14  mils,  varying  from  10 
to  20  mils,  however. 

The  output  of  a  dynamo  —  that  is,  its  electrical 
power — is  generally  calculated  in  watts.  This  is  ob- 
tained by  multiplying  the  total  voltage  by  the  amperes. 
But  as  this  method  of  stating  a  dynamo's  output  admits 
of  uncertain  interpretation,  it  is  best  to  specify  the  volts 
and  amperes  separately. 

In  a  series  machine  the  field  magnet  coils  are  con- 
nected in  series  with  the  outer  circuit.  The  magnetism 
in  the  fields,  therefore,  varies  inversely  as  the  resistance 
of  the  circuit,  being  less  when  the  resistance  is  high 
than  when  it  is  low.  In  a  shunt-wound  machine  the 
field  magnet  coils  are  connected  in  a  shunt  with  the 
outer  circuit.  There  are,  therefore,  two  paths  open  to 
the  armature  current :  one  through  the  field  magnet 
coils,  and  the  other  through  the  outer  circuit.  The 
resistance  in  the  outer  circuit  being  lower  than  that 
of  the  field  magnet  coils,  more  current  goes  by  way  of 
the  outer  circuit  than  goes  round  the  coils,  but  when  the 
resistance  of  the  outer  circuit  is  increased,  more 
current  goes  by  way  of  the  coils,  and  this  raises  the 
magnetic  intensity  of  the  fields.  The  effect  of  this  is  to 
raise  the  voltage  of  the  current,  and  enable  it  to  over- 
come the  extra  resistance.  In  a  compound-wound 
machine  the  field  magnet  coils  are  partly  of  thick  wire 
connected  in  series  with  the  armature  and  outer  circuit, 
while  a  small  wire  of  high  resistance  is  connected  in 
shunt.  This  form  of  machine  may  be  made  to  give 
almost  a  constant  potential  difference  at  the  ter- 
minals. 

Each  style  of  winding  has  its  own  peculiar  advan- 
tages, adapting  it  to  the  kind  of  work  to  be  done  by  the 


CALCULATING   WIRE  FOR  SMALL  DYNAMOS.  81 

machine.  A  shunt-wound  dynamo  becomes  self-regu- 
lating to  a  certain  extent ;  for  as  the  lamps  are  switched 
off  the  resistance  in  the  outer  or  lamp  circuit  becomes 
greater,  and  more  current  is  shunted  through  the  field 
coils,  thereby  generating  a  higher  voltage  to  overcome 
the  increased  resistance,  while  a  compound-wound 
dynamo  is  self-regulating  to  a  still  greater  extent. 

A  rough  rule  for  shunt-wound  machines  with  about 
90  per  cent,  efficiency  is  as  follows  :— Let  the  resistance 
of  the  armature  be  represented  by  1,  that  of  the  outer 
circuit  by  20,  then  that  of  the  field  magnet  circuit  should 
be  400 — that  is  to  say,  the  outer  circuit  should  have  a 
resistance  twenty  times  that  of  the  armature,  and  the 
field  magnet  circuit  should  have  a  resistance  four  hundred 
times  that  of  the  armature.  In  a  series  machine,  the 
field  magnet  coils  should  have  a  resistance  about  two- 
thirds  that  of  the  armature  coil.  In  a  compound  machine, 
the  resistance  of  the  series  coils  should  be  the  same  as 
that  of  the  armature.  In  small  machines  these  propor- 
tions have  to  be  considerably  modified.  In  a  300-watt 
machine— to  give  6  amperes  at  50  volts— the  field  magnet 
resistance  may  be  reduced  to  200  instead  of  400,  and 
this  proportionate  resistance  rapidly  diminishes  with 
each  small  reduction  in  the  size  of  the  machine,  until 
the  smallest  workable  dynamo  will  only  admit  of  the 
resistance  of  the  field  magnet  coils  being  some  twelve  or 
fifteen  times  that  of  the  armature  coil.  It  is  almost 
impossible  to  determine  exactly  the  output  of  such 
small  machines ;  for  apart  from  the  variations  from 
theoretical  rules,  others  are  likely  to  crop  up  through 
differences  in  the  qualities  of  iron  employed,  hardness 
of  wire,  irregular  or  loose  winding,  insulation,  connec- 
tions, size,  form  and  make  of  commutator,  and  quality, 
position,  and  pressure  of  brushes,  etc. 

Properly  designed  castings  for  the  carcase  'of  the 
dynamo  usually  have  ample  space  allowed  for  winding 
sufficient  wire  to  suit  the  electrical  output  of  the 
machine.  If  the  carcase  of  the  machine  has  to  be  forged 
or  cast,  and  the  rings  or  punchings  for  the  armature 


82  DYNAMOS  AND  ELECTRIC  MOTORS. 

made  to  order,  proper  space  must  be  allowed  for  the 
wire.  By  referring  to  the  tables  given  on  pages  78  and 
79,  the  spa<  e  likely  to  be  occupied  by  the  wire  will  be 
found  under  the  heading  "  No.  of  turns  per  inch  " — that 
is,  so  many  turns  of  wire  of  a  given  gauge  will  lie  side 
by  side  in  1  in.  of  space.  The  channel  in  a  shuttle 
armature  must  be  large  enough  to  take  the  required 
wire  without  bulging  beyond  the  cheeks.  The  space 
between  the  outer  edge  of  the  ring  or  drum  armature 
and  the  sides  of  the  tunnel  in  which  it  is  to  work 
should  be  sufficient  to  leave  ^a  in-  between  the  wire  and 
the  sides  after  three  layers  of  the  wire  have  been  wound 
on.  One  layer  is  theoretically  the  best,  but  three  layers 
are  admissible. 

The  length  of  the  field  magnet  cores  may  be  about 
three  or  three  and  a  half  times  their  diameter,  and 
provision  should  be  made  to  admit  of  enough  wire  to 
increase  the  diameter  of  the  core  from  two  and  a  half  to 
three  times.  The  space  to  be  occupied  by  the  wire  may 
be  ascertained  by  estimating  its  length  and  weight  or 
length  Tper  pound,  noting  how  many  turns  to  the  inch 
it  will  run.  Estimate  the  probable  diameter  of  the 
wound  core,  and  find  the  mean  between  this  and  the 
bare  core,  then  multiply  this  by  the  factor  3'14,  and  so 
ascertain  the  number  of  turns  and  the  space  likely  to  be 
occupied  by  the  wire.  Heavy  yokes  and  pole  pieces 
are  always  admissible,  because  dynamos  work  best  when 
the  iron  in  them  is  in  excess  of  that  needed  to  maintain 
magnetic  saturation.  It  is  also  advisable  to  have  a 
larger  carcase  than  will  be  actually  needed  to  furnish 
the  required  output,  since  machines  may  always  be  safely 
worked  to  light  fewer  lamps  than  they  were  designed 
for ;  but  it  is  not  safe  to  work  them  at  a  higher  speed 
to  procure  a  larger  output. 

Before  the  plan  for  winding  the  armature  can  be  drawn 
up,  the  resistance  of  the  outer  circuit — namely,  the  work 
to  be  done  by  the  machine — must  first  be  ascertained. 
If  this  resistance  is  too  low,  a  shunt  machine  will  fail 
to  supply  the  required  current,  and  a  series  machine 


CALCULATING   WIRE  FOR  SMALL  DYNAMOS.  83 

will  burn  its  coils.  If  too  high,  no  current  will  be 
obtained  from  a  series  machine,  and  that  from  a  shunt 
machine  will  be  diminished.  In  large  machines,  care- 
fully wound,  an  efficiency  of  1  volt  per  foot  of  effective 
wire  on  the  armature  moving  at  a  circumferential 
velocity  of  1,250  feet  per  minute  has  been  attained,  but, 
as  has  been  stated,  1  volt  per  yard  is  what  may  be 
expected  from  small  machines.  Although  the  voltage  of 
a  machine  may  be  increased  by  increasing  the  speed  of 
its  armature,  it  is  not  always  safe  to  do  so,  because  an 
increased  voltage  will  send  more  current  round  the  field 
magnet  coils,  and  this  may  dangerously  heat  them.  In  a 
series  machine,  all  the  current  passing  through  the  outer 
circuit  also  traverses  the  field  magnet  coils.  In  a  com- 
pound machine,  the  bulk  of  all  its  current  passes 
through  the  series  coils  and  only  a  fraction  of  it  through 
the  shunt  coils.  In  a  shunt  machine,  only  a  fraction  of 
the  current  passes  through  the  field  magnet  coils.  Con- 
sequently, the  fields  of  the  series  machine  are  not 
magnetised  when  the  outer  circuit  is  open,  and  the 
fields  of  the  shunt  machine  are  then"  most  highly 
magnetised.  When  a  machine  is  run  at  a  higher  speed, 
the  brushes  should  be  given  a  more  forward  lead,  to 
compensate  for  increased  distortion  of  the  field. 

The  wires  for  dynamos  may  be  protected  by  using 
indiarubber  or  gutta-percha  dissolved  either  in  benzole 
or  in  naphtha.  This  solution  will  make  an  elastic 
insulating  varnish,  but  it  is  liable  to  injury  from  oil, 
which  renders  the  varnish  soft  and  sticky.  Shellac 
varnish  is  one  of  the  best  for  the  purpose.  This  is 
made  by  digesting  shellac  in  methylated  spirit,  kept  in 
a  stoppered  glass  jar  in  a  warm  place  for  twelve  hours. 
Green  or  red  sealing-wax  digested  in  warm  methylated 
spirit  is  also  used  as  an  insulating  varnish. 

Few  persons  can  get  the  calculated  amount  of  wire 
on  an  armature,  although  a  full  allowance  has  been 
made  for  slack  winding.  To  take  an  armature  in 
one  hand  and  let  the  wire  run  through  the  fingers  of  the 
other,  drawing  it  more  or  less  tight,  winding  as  one 


84  DYNAMOS  AND  ELECTRIC  MOTORS. 

would  wind  up  a  ball  of  string,  sometimes  working 
evenly,  sometimes  not,  will  not  do.  To  wind  an  arma- 
ture properly,  especially  if  of  either  the  drum  or  ring 
type,  is  work  for  two  people.  Even  a  shuttle  armature 
should  not  be  attempted  by  one  person  unless  he  is  an 
experienced  winder  ;  and  even  then  he  will  wish  he  had 
three  hands. 

After  the  wire  has  been  properly  paraffin-waxed  and 
drained,  it  should  be  wound  on  as  tight  as  possible, 
without,  of  course,  breaking  it.  Any  wire  that  is  not 
perfectly  straight,  or  is  in  the  least  respect  faulty  should 
be  driven  well  into  place  by  means  of  a  small  wooden 
hammer  or  by  a  small  wooden  stick,  neatly  squared  and 
smoothed  at  the  end,  and  used  as  a  punch.  Every  wire 
should  be  made  to  go  as  .near  to  its  neighbour  as  possible. 
It  will  be  seen  that  winding  an  armature  properly  is  no 
light  work. 

Cheap  wire  is  very  bad,  for  two  reasons— one  is 
that  the  wire  itself  has  a  comparatively  low  percentage 
of  copper,  and  wire  should  not  be  used  that  has  less  than 
97  per  cent,  as  it  gives  the  armature  a  needlessly  high 
resistance.  The  other  is  that  cheap  wire  has  bad, 
thick  cotton  for  its  covering,  and  consequently  occupies 
space  wastefully.  Another  source  of  trouble  is  thick, 
clumsy  taping.  There  should  be  just  enough  to  ensure 
perfect  insulation,  and  no  more.  Bad  taping  takes  up  a 
lot  of  room,  and  space  is  precious  to  a  winder  of 
armatures.  Remember  this,  and  do  not  be  .afraid  of 
using  the  wooden  hammer. 

In  treating  the  subject  of  calculating  the  length  of 
wire  for  armatures,  two  types  only  will  be  taken — viz., 
the  Siemens  H-girder,  or  shuttle  armature  (Figs.  83  and 
84)  and  the  cog-ring  armature  (Figs.  85  and  86),  as  un- 
doubtedly they  are  the  best  types  of  armatures  for  small- 
sized  dynamos  ;  the  former  for  the  very  small  sizes,  and 
the  latter  for  somewhat  larger  ones.  They  are  also  the 
easiest  kinds  to  wind  and  correct,  and  are  therefore  very 
suitable  for  amateur  workers. 

As  an  illustration,  it  would  be  best  to  take  a  sample 


CALCULATING  WIRE  FOR  SMALL  DYNAMOS.  85 

armature,  fix  upon  a  certain  gauge  of  wire,  and  follow  up 
the  working  to  get  at  the  weight  and  length  of  wire 
required ;  by  this  means  the  reader  will  have  an 
example  at  hand  to  work  from  in  cases  of  armatures  of 
other  sizes. 

The  first  example  will  be  a  laminated  shuttle  arma- 
ture, 2£  in.  long,  l£  in.  in  diameter  (Figs.  83  and  84), 


{.-  ,*•_.    „ 

Fig.  83.— Section  of  Shuttle  Armature. 

having  the  web  flush  with  the  ends.    An  armature  of  this 
size  would  probably  have  wire  spaces  I  in.  wide,  and  by 


Fig.  84.— Side  View  of  Shuttle  Armature. 

making  the  segment  of  the  circular  area  form  a  rectangle 
of  equal  area,  as  shown  by  the  dotted  lines  in  Fig.  83,  the 
wire  space  would  be  £  in.  deep,  leaving  f  in.  for  the 
thickness  of  the  web.  In  calculating  shuttle  armatures 
the  shaft  need  not  be  taken  into  consideration,  as  it  does 
not  affect  the  amount  of  wire  that  will  go  into  the 
channels,  though  it  makes  the  winding  at  the  ends 
irregular,  which  cannot  be  helped  ;  the  slight  extra 


86          DYNAMOS  AND  ELECTRIC  MOTORS. 

length  required  through  this  irregularity  can  in  practice 
be  neglected. 

The  next  operation  will  be  to  make  a  sketch  of  the 
side  of  the  armature,  as  in  Fig.  84,  where  the  full  line 
will  represent  the  last  coils  of  wire ;  then  by  setting 
£  in.  off  at  each  end,  the  longest  coil  is  obtained  as  a 
rectangle.  (See  the  dotted  lines  in  Fig.  84.)  The  next 
thing  to  find  is  the  mean  length  of  all  the  turns.  This 
will  be  the  shortest  turn,  added  to  the  longest  turn, 
divided  by  2.  The  shortest  length  is  one  of  the  turns  in 
the  first  layer,  and  will  be,  of  course,  rather  more  than 
(2  X  2i)  +  (2  x  I)  =  52  ;  the  longest  length  will  be 
the  length  of  the  sides  of  the  rectangle  in  dotted  lines 


Fig.  85. — Section  of  Cog-ring  Armature. 

(Fig.  84),  which  was  shown  to  represent  the  longest 
coil ;  then  the  longest  turn  will  be  (2  X  3J)  +  (2  X  li) 
=  9 1 ;  so  the  mean  length  of  all  the  coils  will  be 
5J  +  9J  -*-2  =  7f  in. 

For  this  example,  No.  20  S.W.G.  cotton-covered  wire 
will  be  taken  to  wind  the  armature.  Upon  looking  in 
the  tables  (p.  "78),  it  will  be  found  that  this  wire  can  be 
coiled  twenty- three  coils  to  the^  linear  inch.  Should 
there  be  no  tables  at  hand,  take  a  spare  piece  of  wire  of 
the  gauge  to  be  used,  and  coil  it  round  neatly  on  any- 
thing smooth,  and  count  how  many  coils  go  to  an  inch. 
As  the  wire  space  is  |  in.  wide,  and  £  in.  deep,  it  can  be 
assumed  that  twenty  coils,  eleven  layers  deep,  can  be  got 
into  the  space  ;  this  will  make  220  coils  in  all.  Now  it 
has  been  found  that  the  average,  or  mean  coil  of  all  the 
coils  is  7|  in.  long ;  therefore  the  total  length  of  wire 
will  be  220  X  7|  =  1,705  in.,  or  47  yds.,  1  ft, 
1  in. — say  47  yds.  No.  20  S.W.G.  cotton-covered 


CALCULATING   WIRE  FOR  SMALL  DYNAMOS.  87 

wire  goes  80  yds.  to  the  pound,  so  the  amount 
of  wire  for  this  armature  would  be  7  yds.  over 
\  lb.,  or  say  J  Ib.  Of  course,  it  will  be  observed  that 
ehould  the  armature  be  solid,  with  the  web  set 
back  from  the  ends,  much  less  wire  can  be  got  on,  also 
the  winding  would  be  neater  and  more  compact  if  the 
shaft  did  not  run  through  the  web. 

For  the  other  example  a  laminated  cog-ring  arma- 
ture will  be  taken,  5  in.  in  diameter,  3  in.  deep,  having 
twelve  cogs ;  wire  spaces  f  in.  wide  and  |  in.  deep,  with 


~VT 

Fig.  86.— Side  View  of  Cog-ring  Armature. 


the  core  of  the  armature  |  in.  thick  at  the  wire  spaces 
and  £  in.  thick  at  the  cogs.  (See  Figs.  85  and  86.)  This 
armature  it  is  proposed  to  wind  with  No.  12  S.W.G.  cotton- 
covered  wire.  The  mode  of  operation  is  very  similar  to 
the  example  above,  one  whole  coil  being  calculated  first. 
A  section  of  the  armature  core  through  a  wire  space 
must  be  drawn  as  in  Fig.  85  ;  then  setting  off  the  f  in., 
the  depth  of  the  wire  space  all  round,  the  longest  mean 
coil  is  found  as  a  rectangle,  as  shown  by  dotted  lines. 

Proceeding  as  before,  the  mean  length  of  all  the 
coils  is  found ;  thus  the  shortest  (2  X  3)  +  (2  X  f ) 
=  6  i  in. ;  and  the  longest  (.2  X  3J)  +  (2  X  U)  =  9*  ; 
then  the  mean  coil  will  be  8|  in.  long.  The  wire 


88          DYNAMOS  AND  ELECTRIC  MOTORS. 

tables  (p.  78)  show  that  eight  coils  of  No.  12  S.W.G. 
cotton-covered  wire  go  to  the  linear  inch ;  so  in 
the  space  f  in.  X  f  in.  there  will  be  room  for  five 
coils,  three  layers  deep,  which  will  make  fifteen  coils  in 
all.  As  the  mean  coil  is  8J  in.  long,  the  total  length  will 
be  15  X  8£  =  123|  in- ;  but  as  there  are  twelve  separate 
coils  on  the  armature  the  total  length  of  wire  for  the 
whole  armature  will  be  123f  X  12  =  say  41  yds.  No.  12 
S.W.G.  cotton-covered  wire  runs  8'8  yds.  to  the  pound ; 
so  between  4J  Ib.  and  4J  Ib.  will  be  enough. 

A  simple  way  to  determine  the  mean  length  of  the 
coil  is  to  add  together  any  two  adjacent  sides  of  the 
rectangles  forming  the  longest  and  shortest  coils. 
Taking  the  first  example  (p.  85),  shortest  coil  = 
(2  X  2£  in.)  +  (2  X  f  in.)  j  longest  coil  =  (2  X  3£  in.) 
+  (2  X  If  in.) ;  mean  coil  =  half  the  sum  of  these. 
Now,  the  shortest  coil  may  be  written  :  2  (2J  in.  +  |  in.). 
Similarly,  the  longest  coil  =  2  (3J  in.  +  If  in.) :  and 
combining  the  two,  and  talking  half  the  sum  for  the 
mean  coil,  we  get 

${(2j  in.  +  f  in.)  +  (3j  in.  +  If  in.)} 

* 

which  is  equal  to  mean  coil ;  and  by  cancelling  the 
multiplier  and  divisor  of  fraction,  we  have  left,  2J  in.  + 
|  in.  +  3J  in.  +  If  in.  =  mean  =  6  in  -f  1^  in  =  7J  in.; 
and  in  the  second  example,  3  in.  +  f  in.  -f-  3f  in. 
+  li  in.  =  mean  =  6|  in.  +  1J  in.  =  8|  in. 


CHAPTER   VII. 

AILMENTS  OF  SMALL  DYNAMO-ELECTRIC  MACHINES,  THEIR 
CAUSES  AND  CUHES. 

To  localise  the  faults  common  to  dynamos,  we  [shall 
require  a  battery  of  three  or  four  cells  of  a  strong 
and  constant  type,  a  galvanometer  or  current  detector, 
such  as  those  used  by  electric-bell  fitters,  and  a  mag- 
netised needle  or  a  pocket  compass.  To  repair  the 
faults  we  shall  need  a  soldering-iron,  some  soft  solder, 
and  some  resin  to  solder  faulty  joints  ;  a  pair  of  stout 
pliers,  a  screwdriver,  small  spanners  to  fit  the  nuts 
on  the  machine,  and  some  soft  cotton  or  tape,  or  both, 
well  soaked  in  melted  paraffin  wax. 

The  best  battery  for  the  purpose  is  the  single  fluid 
bichromate  battery — that  is,  a  battery  composed  of  jars 
or  wide-mouthed  bottles  of  glass  or  stoneware,  each 
holding  a  pint.  Each  jar  contains  a  plate  of  amal- 
gamated zinc  between  two  plates  of  carbon,  and  is 
charged  with  a  liquid  composed  of  3  ozs.  bichromate  of 
potash  dissolved  in  a  pint  of  water,  and  3  ozs.  of 
sulphuric  acid.  This  liquid  must  be  allowed  to  cool 
before  the  zinc  plate  is  placed  in  it. 

The  zinc  plate  in  one  cell  must  be  connected  to  the 
carbon  plate  in  the  next  cell  by  a  stout  copper  wire,  say 
No.  16  s.w.a,  and  all  the  cells  must  be  thus  con- 
nected so  as  to  leave  one  zinc  plate  free  at  one  end  of 
the  row,  and  one  carbon  plate  free  at  the  other  end  of 
the  row.  About  2  ft.  of  No.  18  or  No.  20  S.W.G.  wire, 
attached  to  these  end  plates  by  suitable  binding-screws, 
will  serve  to  connect  the  battery  with  the  galvanometer 
and  the  machine.  A  steel  darning-needle,  magnetised 
by  rubbing  it  on  a  permanent  magnet,  and  suspended  by 
a  piece  of  cotton  to  hang  horizontally,  witt- serve  as  a 


QO          DYNAMOS  AND  ELECTRIC  MOTORS. 

substitute  for  a  pocket  compass.  With  this  apparatus 
the  following  faults  may  be  localised. 

If  the  cores  of  the  magnets  are  not  magnetised,  no 
current  will  be  generated  in  the  armature  coil.  If  one 
of  the  field  magnet  coils  of  an  overtype  or  undertype 
machine  is  wound  in  the  wrong  direction,  both  pole 
pieces  may  have  a  like  magnetism,  and  the  same  negative 
result  will  be  obtained.  One  pole  piece  must  have 
an  opposite  polarity  to  the  other.  The  compass  needle 
being  held  near  the  pole  pieces  of  an  ordinary  two-pole 
machine,  one  of  them  should  attract  the  north  pole 
of  the  needle,  and  the  other  repel  it.  The  machine 
should  be  tested  in  this  way  whilst  the  armature  is  at 
rest,  and  also  when  it  is  running.  If  the  coils  are 
wrongly  connected,  there  may  be  a  similar  result.  If 
the  compass  needle  does  not  indicate  any  magnetism, 
or  only  a  feeble  magnetism,  it  may  be  assumed  that  the 
pole  pieces  are  not  magnetised. 

The  whole  of  the  armature  current  in  a  series  machine, 
and  a  portion  of  it  in  a  shunt  machine,  will  be  em- 
ployed in  maintaining  the  magnetism  of  the  field ;  we 
must  be  careful  so  to  convey  it  through  the  field-magnet 
coils  as  to  retain  the  polarity  of  the  cores  induced 
initially  by  the  battery  current. 

A  series-wound  dynamo  employed  in  depositing 
metals  from  their  solutions,  or  in  charging  accumu- 
lators, is  liable  to  have  its  poles  reversed  by  a  back 
current  from  the  plating-vat  or  the  accumulator  cells. 
For  this  reason  series  dynamos  are  not  suitable  for 
such  work.  The  polarity  of  the  core  is  also  reversed 
when  current  is  sent  through  its  coils  from  a  battery,  or 
another  dynamo,  to  run  the  machine  as  an  electric  motor. 
Compound-wound  machines  are  also  liable  to  a  reversal 
of  their  magnetism  from  a  similar  cause,  owing  to  a 
high  reverse  current  passing  through  the  series  coils.  A 
shunt-wound  machine  can  only  be  reversed  by  such 
means  when  its  field-magnet  coils  are  wrongly  con- 
nected to  a  battery ;  therefore,  a  shunt-wound  machine 
should  always  be  used  for  charging  accumulators  and 


AILMENTS  OF  SMALL  DYNAMO  MACHINES,   gi 

for  electro-depositing  work.  This  altered  polarity  of 
the  field-magnets  may  be  detected  by  the  compass 
needle  being  held  to  them,  and  the  original  magnetism 
can  be  restored  by  the  means  adopted  at  first  for 
magnetising  the  cores. 

Magnetism  neutralised,  which  may  also  be  named 
short-circuiting  the  magnetic  poles,  occurs  when  the 
poles  are  bridged  by  a  mass  of  iron,  as  when  an  under- 
type  field  is  bolted  direct  to  an  iron  bed-plate,  or  an  over- 
type field  is  bridged  by  an  iron  plate  secured  to  the  pole 
pieces.  When  an  air  space  is  left  between  the  polar 
extremities  of  a  horseshoe  magnet,  the  magnetic  lines 
of  force  may  be  supposed  to  stretch  across  from  one 
pole  piece  to  the  other,  and  are  then  in  a  position 
to  pass  through  the  armature  coils.  But  when  a 
piece  of  iron  bridges  these  polar  extremities,  the  greater 
number  of  the  magnetic  lines  pass  by  way  of  this 
bridge,  and  so  are  diverted  through  the  armature  from 
their  useful  path,  and,  as  there  are,  therefore,  few 
or  no  lines  of  force  passing  through  the  armature, 
there  will  be  a  very  faint  current  from  the  machine, 
or  none  at  all. 

The  field-magnets  have  been  short-circuited  by 
placing  a  guard  of  thick  iron  over  the  armature  gap 
The  guard  over  the  armature  space  of  an  overtype 
dynamo  should  be  of  zinc  or  gun-metal ;  and  if  it  is 
necessary  to  have  a  metal  bed-plate  for  an  undertype 
dynamo,  brackets  of  gun-metal  or  of  zinc  should  be 
interposed  between  the  magnet  poles  and  the  iron  of 
the  bed-plate. 

If  the  machine  does  not  give  a  current  or  the  desired 
effect,  though  the  magnetic  properties  of  the  field  have 
been  tested  as  directed  and  found  perfect,  leakage  or 
short-circuiting  of  the  coils  may  be  suspected.  To  detect 
this  we  must  employ  a  battery  and  galvanometer,  as 
before  explained.  Leakage  most  frequently  takes  place 
between  the  wire  of  the  coils  and  the  iron  of  the  field 
magnets  or  the  armature.  Perhaps  ^the  rough  corners 
on  the  castings  have  not  been  made  smooth.  Perhaps 


92          DYNAMOS  AND  ELECTRIC  MOTORS. 

the  iron  has  not  been  coated  with  a  sufficiently  thick 
layer  of  varnish,  paraffined  tape,  or  calico  ;  or  the  wire 
has  been  pulled  tight  over  these  rough  or  unprotected 
parts,  and  the  insulation  has  been  cut  through,  thus 
bringing  bare  copper  into  contact  with  bare  iron.  As  a 
consequence,  the  current  takes  a  short  cut  by  way  of 
the  iron  instead  of  going  through  all  the  coil  of  wire, 
and  the  result  is  seen  in  a  diminished  output  from  the 
machine. 

-  The  following  is  a  rough-and-ready  means  fre- 
quently adopted  for  discovering  this  fault.  Disconnect 
the  ends  of  the  field  magnet  coils  from  their  terminals, 
and  connect  one  end  of  the  coils  to  one  terminal  of  the 
battery.  Then  take  a  long  exploring  wire  and  connect 
to  the  opposite  terminal  of  the  battery,  and  with  the 
free  end  of  this]  scrape  the  iron-work  and  metal- work  of 
the  machine  at  several  points.  If  any  bare  part  of  the 
wire  coil  is  touching  the  bare  iron  of  the  machine,  a 
bright  spark  will  be  seen  to  flash  from  the  part  of  the 
machine  touched  with  the  exploring  wire.  By  discon- 
necting the  two  coils  from  each  other  and  testing  each 
separately,  the  faulty  one  may  be  discovered.  The 
armature  coils  may  be  tested  in  a  similar  manner— in 
fact,  they  must  be  tested  for  leakage  as  well  as  those  of 
the  fields.  It  is  advisable,  however,  in  both  cases  to 
place  the  galvanometer  in  circuit  by  connecting  the  bat- 
tery to  it,  and  then  to  connect  the  exploring  wire  to  the 
galvanometer.  If  the  needle  moves,  it  shows  that  there 
is  a  leakage,  however  small  or  large  this  may  be,  but  the 
rough  test  will  only  reveal  a  bad  leakage. 

Leakage  of  another  form  may  occur  between  adjacent 
turns  or  layers  of  wire  in  the  same  coil,  and  is  due  to  the 
stripping  off  of  the  insulation,  from  some  such  cause  as 
hammering  the  coils  to  get  them  in  their  proper  places, 
or  from  pulling  them  too  tight.  If  a  machine  is  over- 
driven, or  if  a  series  machine  is  short-circuited,  the 
insulating  covering  may  get  burnt  off,  and  thus  the 
coils  become  short-circuited. 

This  fault  can  only  be  discovered  by  means  of  the 


AILMENTS  OF  SMALT.  DYNAMO  MACHINES.    93 

galvanometer  in  circuit  with  the  battery.  Each  coil 
must  be  placed  in  circuit  separately,  the  deflections  of  the 
galvanometer  needle  noted,  and  these  compared.  Equal 
lengths  of  wire  should  have  equal  resistances,  and  this 
should  be  indicated  by  equal  deflections  of  the  galvano- 
meter needle.  If  the  needle  swings  over  much  farther 
when  one  coil  is  in  circuit  than  when  a  similar  coil  of  the 
same  length  is  tested,  we  may  expect  that  coil  to  be 
short-circuited  somewhere,  because  it  offers  a  less  resist- 
ance than  the  perfect  coil.  Each  coil  of  the  armature 
should  be  unsoldered  from  the  commutator  bars  and 
tested  separately  in  comparison  with  the  others.  All 
faulty  coils  must  be  unwound  and  the  fault  repaired  by 
winding  paraffined  cotton  or  tape  over  the  bare  spot. 

Leakage  sometimes  occurs  between  the  commutator 
bars  and  the  spindle,  or  between  the  sections  of  the  com- 
mutator itself,  or  between  the  brush-holders  and  other 
parts  of  the  machine.  Any  of  these  leakages  may  be 
detected  by  the  galvanometer  and  one  or  more  cells  of 
the  battery.  The  commutator  bars  may  be  accidentally 
placed  in  contact  with  the  spindle  by  using  long  screws. 
To  detect  this  fault,  attach  one  battery  wire  to  the 
spindle  and  the  other  to  the  galvanometer,  then 
touch  each  bar  with  the  free  wire  from  the  galvano- 
meter and  watch  the  indications  of  the  needle.  If 
the  needle  moves  when  a  bar  is  touched,  that  bar  is 
in  contact  with  the  spindle.  Any  faulty  screw  must 
be  withdrawn,  and  a  shorter  one  used.  If  the  bars  are 
accidentally  connected  by  metal  dust,  or  by  expansion  of 
the  sections  whilst  heated,  this  fault  may  be  detected  by 
placing  one  wire  from  the  battery  on  one  bar  and  the 
wire  from  the  galvanometer  on  the  next  bar.  The  coils 
must  be  disconnected  from  the  bars  whilst  this  is  being 
done.  Sometimes  the  brush-holders  are  not  insulated 
from  the  machine.  This  fault  may  be  detected  by 
testing  each  separately  with  the  body  of  the  machine 
in  circuit,  and  then  testing  the  two  together.  If  all 
is  right,  no  current  should  pass  between  them  and  the 
machine  or  between  the  two  holders  when  the  brushes 


94          DYNAMOS  AND  ELECTRIC  MOTORS. 

are  off,  and  they  are  disconnected  from  the  outer  circuit. 
Perfect  insulation  at  these  points  is  of  the  greatest 
importance. 

A  machine  tested  at  all  points  indicated  above  and 
found  all  right,  or  the  detected  faults  put  right,  and  yet 
that  will  not  give  satisfaction,  may  have  a  fault  in  the 
brushes.  All  brushes,  in  any  type  of  machine,  should  be 
held  in  suitable  brush-holders  fixed  to  an  insulated 
rocker,  or  in  insulated  sleeves  attached  to  such  a  rocker. 
Fixed  brushes  on  standards,  or  on  blocks  attached  to  the 
machine,  give  much  trouble,  since  they  can  only  be  ad- 
justed by  the  exercise  of  much  time  and  patience,  and  even 
then  cannot  be  trusted  to  remain  right  for  any  length  of 
time.  The  most  inexpensive  and  efficient  material  for 
brushes  in  small  dynamos  is  copper  gauze,  cut  into  strips 
of  suitable  width  and  length,  and  formed  into  pads  by 
soldering  the  strips  together  at  the  ends  to  go  in  the 
brush-holders.  As  these  pads  have  very  little  elasticity 
in  them,  it  is  advisable  to  back  them  with  a  strip  of  spring 
steel,  German  silver,  or  brass,  so  as  to  ensure  enough 
pressure  to  keep  them  in  good  contact  with  the  commu- 
tator. Machines  frequently  fail  because  of  having  hard 
brass  brushes,  which  press  unevenly  on  the  commutator, 
or  get  thrown  out  of  contact  when  the  machine  is  driven 
at  a  high  speed.  Pads  of  copper  gauze  bear  and  wear 
more  evenly  than  springs  of  hard  brass. 

When  these  pads  are  fixed  to  a  rocker,  they  may  be 
easily  adjusted  to  any  position.  The  theoretically  right 
position  for  the  brushes  is  for  their  ends  to  bear  on  the 
commutator  bars  opposite  the  centre  of  the  open  spaces 
between  the  field  magnets.  The  position  practically 
right  is  always  in  advance  of  this,  because  the  armature 
current  distorts  the  lines  of  force  in  the  magnetic  field. 
This  forward  position  or  lead  of  the  brushes  must  be 
found  by  experiment,  because  it  varies  with  the  type  and 
speed  of  every  machine.  As  a  rule,  the  highest  speed 
demands  the  most  forward  lead.  If  the  machine  is  con- 
nected to  the  thick  coil  of  a  suitable  ammeter  when 
driven  at  the  required  speed,  and  the  brushes  are 


AILMENTS  OF  SMALL  DYNAMO  MACHINES.    95 

moved  until  the  best  effects  are  noted  by  the  deflec- 
tion of  the  needle,  this  will  be  the  best  position  for  the 
brushes. 

Sparking  at  the  Brushes. — The  machine  may  run  all 
right,  and  give  a  fairly  good  current  for  a  short  time, 
but  there  may  be  much  sparking  at  the  brushes,  burn- 
ing them  away  and  burning  pits  in  the  commutator. 
This  shows  defective  construction  or  bad  adjustment 
of  the  brushes.  The  likely  faults  in  construction 
are  :  Coils  of  a  varying  length  and  resistance  on  the 
armature,  insufficient  resistance  in  the  field  magnet 
coils,  or  leakage  between  the  armature  coils  and 
the  carcase  of  the  machine.  This  last  defect  may  be 
found  by  examining  the  armature  coils.  Perhaps  these 
touch  the  iron  occasionally,  and  rub  off  the  insulating 
coating.  This  may  be  due  to  too  much  end-shake  of  the 
armature  spindle,  to  a  worn  bearing,  or  to  a  loose 
bearing  allowing  the  armature  to  wobble. 

A  small  washer  on  the  spindle  will  correct  too  much 
end-play,  tightening  the  nuts  will  remedy  a  loose 
bearing,  but  a  worn  bearing  must  be  bushed  with 
brass  to  cure  side-shake.  If  leakage  occurs,  the  worn 
spot  should  be  coated  with  varnish  worked  in  well 
between  the  folds  of  the  wire.  Sparking  may  indicate 
that  too  much  work  is  being  thrown  on  the  machine. 
Sparking  due  to  bad  adjustment  of  the  brushes  can 
be  cured  by  altering  their  lead,  as  described  in  the 
previous  section  (p.  94). 

Broken  Armature  Wire.  —  Such  a  wire  can  be 
mended  as  follows  : — If  it  is  outside  the  winding,  bare 
and  clean  the'  two  ends,  twist  and  solder  them  together, 
then  paint  the  joint  over  with  either  Brunswick  black  or 
red  sealing-wax  varnish.  If  it  is  in  the  winding,  bare 
and  bevel  the  two  ends,  tin  the  bevels,  and  sweat  the 
joint  together ;  then  work  up  to  as  near  the  size  of 
the  wire  itself  as  possible,  relap  the  joint  with  silk, 
and  dip  it  in  melted  paraffin  wax,  or  paint  it  over 
with  Brunswick  black. 

Sunning  Hot.— Some   of   the   best   designed   and 


96          DYNAMOS  AND  ELECTRIC  MOTORS. 

constructed  machines  will  get  too  warm  after  a  day's  run 
on  heavy  work.  The  passage  of  an  electric  current  through 
the  wire  coils  will  always  warm  them  more  or  less,  and 
much  of  this  rise  of  temperature  is  unavoidable.  When 
the  temperature  rises  considerably,  as  when  the  field 
magnet  coils  feel  quite  hot  if  touched  by  the  hand,  there 
is  always  a  serious  loss  in  heating  the  wires,  because 
hot  wires  offer  more  resistance  to  the  current  than  cool 
wires.  The  main  cause  of  this  excessive  heating  is  an 
employment  of  wires  too  small  to  carry  the  current 
properly ;  or,  in  other  words,  the  machine  is  required 
to  do  more  work  than  it  is  properly  capable  of.  The 
remedy  here  is  clear  enough.  But  sometimes  the  heating 
of  a  machine  is  due  to  defective  construction,  or  it  may 
be  due  to  leakage.  Solid  iron  armatures,  and  laminated 
armatures  which  are  not  insulated,  may  get  unbearably 
hot  in  a  short  time,  because  of  cross  or  eddy  currents 
circulating  in  the  mass  of  iron  from  end  to  end  of 
the  armature. 

When  the  laminations  are  separated  from  each  other 
by  an  insulating  substance  (even  a  thin  coat  of  varnish 
is  sufficient),  these  currents  are  broken  up,  and  cannot 
travel  from  end  to  end.  Machines  with  solid  iron 
armatures,  or  with  badly-insulated  laminations,  will 
get  hot  enough  to  melt  the  soft  solder  connections  at 
the  commutator  and  distort  the  commutator  sections. 
In  series  and  compound  machines  leakage  across  the 
brushes  will  also  heat  the  coils  injuriously.  Short- 
circuiting  a  series  machine  may  seriously  damage  it, 
by  charring  the  insulating  covering  of  the  wires. 

These  are  the  most  common  ailments  of  small 
dynamos.  Others  there  are,  but  it  will  often  be  found 
that  these  are  due  only  to  faulty  workmanship  or  to 
wear  and  tear. 

It  may  be  useful  here  to  say  a  few  words  as  to  the 
possibility  of  receiving  shocks  from  dynamos.  There 
cannot  be  any  serious  shock  to  a  person  handling  a 
dynamo  giving  a  current  of  low  voltage.  Neither  can  a 
person  receive  a  shock  merely  by  touching  the  machine 


AILMENTS  OF  SMALL  DYNAMO  MACHINES.    97 

with  one  hand,  provided  the  machine  as  a  whole  is 
insulated  from  the  ground,  because  the  body  does  not  then 
form  a  link  in  a  closed  electrical  circuit.  It  is  unsafe 
to  meddle  with  large  dynamos,  or  with  any  part  of  an 
electric  light  circuit  in  a  large  installation,  even  to 
touching  it  with  one  hand  only,  unless  you  are 
thoroughly  acquainted  with  it,  because  of  the  uncer- 
tainty of  knowing  when  the  mere  act  of  touching  may 
complete  a  circuit. 

The  general  attention  which  a  dynamo  requires  is 
similar  to  that  needed  by  all  high-speed  machines.  Keep 
all  bearings  and  wearing  parts  clean  and  properly  oiled. 
See  that  the  driving-belt  is  wide  enough  to  take  a  good 
grip  on  the  pulley,  and  thus  maintain  a  good  speed  with- 
out undue  tightness.  It  must  also  be  remembered  that, 
in  addition  to  the  bearings,  the  commutator  and  brushes 
are  the  wearing  parts  of  the  machine.  The  brushes  must 
be  adjusted  to  the  proper  angle,  as  before  explained. 
Sparking  wears  away  brushes  and  commutator  very 
fast,  and  thus  will  demand  frequent  adjustment  of  the 
brushes  to  keep  them  bearing  on  the  best  part  of  the 
commutator.  When  the  brushes  have  cut  grooves  in 
the  commutator  it  is  necessary  to  re-true  the  furrowed 
part,  and  sometimes  to  put  in  a  new  segment. 


CHAPTER  VIII. 

SMALL  ELECTRIC  MOTORS  WITHOUT  CASTINGS. 

THE  little  model  shown  at  Fig.  87,  if  made  according 
to  the  following  instructions,  requires  no  castings  and 
no  lathe  for  its  successful  construction.  It  is  also 


Fig.  87. — Simple  Electric  Motor  complete. 

within  the  reach  of  the  younger  readers  of  this  book 
who  have  an  idea  of  using  a  few  tools,  and  will 
exercise  a  little  ingenuity  and  patience.  The  motor, 
when  complete  and  judiciously  painted  with  such 
simple  colours  as  red  sealing-wax  varnish  and  Bruns- 
wick black,  looks  very  presentable,  to  say  nothing  of 
its  use  in  illustrating  the  laws  of  electro-magnetism. 

For  the  field  magnet  get  a  piece  of  f  in.  round 
wrought  iron  4£  in.  long,  as  soft  as  possible,  and  bend 
it  into  the  form  of  a  horse-shoe,  with  the  ends  }  in. 
apart  on  the  inaide ;  go  over  it  with  a  file  to  take  tha 


ELECTRIC  MOTORS  WITHOUT  CASTINGS.      99 

roughness  off,  and  then  file  up  the  two  ends  true  and 
square  one  with  the  other.  Cut  a  long  strip  of  paper 
— i-in.-wide  newspaper  will  do — and  paste  it  well, 
and  wind  it  round  the  horse-shoe  until  there  are  about 
three  thicknesses  on  all  over,  except  within  i  in. 
from  the  ends ;  paste  the  outside  of  the  paper  all 
over,  and  go  over  it  with  the  fingers  to  get  it  even  ; 
when  this  is  dry  give  it  a  coat  of  Brunswick  black. 
Thin  magnet  does  not  require  any  bobbins,  so  we 


Fig.  88.— Side  Elevation  of  Field  Magnet  and  Block. 

can  go  straight  on  winding  it  with  some  No.  28  S.W.G. 
silk-covered  copper  wire.  Begin  just  short  of  the 
edge  of  the  paper  cover,  with  a  half  hitch,  leaving 
the  end  about  6  in.  long ;  wind  the  wire  on  close  and 
even  until  reaching  the  other  end,  just  within  the  edge 
of  the  paper;  then,  still  winding  the  same  way,  go 
back  over  the  first  coils,  but  be  careful  that  the  wire 
does  not  slip,  and  that  the  second  row  does  not  sink 
between  the  first. 

After  going  back  about  \  in.  or  so,  fix  the  end 
by  giving  two  or  three  turns  on  the  opposite  leg  of 
the  magnet  or  by  any  other  way  that  may  be  con- 
venient, and  give  the  whole  magnet  another  coat  of 


ioo        DYNAMOS  AND  ELECTRIC  MOTORS. 

Brunswick  black;  let  this  get  dry  (it  does  not  take 
long),  and  go  ahead  again,  always  applying  a  fresh  coat 
of  varnish  when  an  end  is  reached.  By  taking  care  in 
turning,  and  repeating  the  coats  of  Brunswick  black, 
all  danger  of  slipping  will  be  avoided. 

The  wire  coils  will  not  lie  close  together  on  the  out- 
side of  the  bent  part  of  the  iron  core.    Keep  them  close 


Fig.  89.— Plan  of  Field  Magnet  and  Block. 

on  the  inside,  however,  and  make  them  radiate  nicely 
for  the  sake  of  appearance  ;  winding  round  the  bent 
part  in  this  way  will  not  interfere  with  the  working. 

When  the  winding  has  been  continued  till  the 
coils  laid  measure  about  |  in.  in  diameter  all  over, 
finish  off  at  the  opposite  end  from  which  you  began 
by  tying  a  piece  of  thread  close  up  to  the  finish, 
leaving  another  6-in.  length  of  wire.  Wind  the 
thread  in  different  directions,  and  fasten  it  off  with  a 
knot.  See  that  the  ends  of  the  iron  core  are  flat 
and  bright.  (See  Figs.  88,  89,  and  90.) 

For  the  armature  take  a  small  piece  of  soft 
wrought  iron,  Ifi  in.  long,  \  in.  thick,  or  a  little 


ELECTRIC  MOTORS  WITHOUT  CASTINGS.     101 

thicker,  and  f  in.  wide  ;  file  it  smooth  all  over,  and 
take  off  all  sharp  edges.  Get  a  short  strip  of  paper, 
f  in.  wide,  and  paste  it  Touri,d  the  exact  middle  of  the 
iron  until  there  are  thwfe'-'Ot  four  thicknesses  on. 
Give  the  paper  a  coat  of  Brunswick  Wack.  and  let 
it  dry. 

Now  begin  to  wind  the  armature,  using  No.  36  s.w.o 
silk-covered  copper  wire.    Take  great  care  in  winding 


Fig.  90.— Front  Elevation  of  Field  Magnet  and  Clock. 


the  armature,  turning  backwards  and  forwards  as  with 
the  field  magnet,  giving  each  layer  a  coat  of  Bruns- 
wick black,  and  wind  on  as  much  wire  as  the  armature 
will  accommodate.  The  more  neatly  the  work  is  done 
the  more  wire  will  be  got  on,  and  the  better  will  be 
the  results  ;  finish  off  in  the  middle,  and  leave  tags 
at  each  end  about  2  in.  long.  See  that  the  coils  are 
not  more  than  £  in.  across  in  front,  or  the  magnet  will 
rub  them.  Fig.  91  (p.  102)  will  show  what  is  meant. 
While  winding  the  armature,  it  may  be  tried  in  different 
positions  against  the  magnet,  to  see  that  the  coils  are 
quite  clear  of  other  parts,  for  if  they  do  not  touch 
while  the  armature  is  against  the  magnet,  it  may  be 
assumed  that  they  will  be  all  right  afterwards. 


loz        DYNAMOS  AND  ELECTRIC  MOTORS. 

The  brushes  are  simply  two  thin  copper  strips,  3  in. 
long  and  ^  in.  wide,  bent  to  the  required  shape,  with 
a  piece' trf  silk-covered,  'coppe?  wire  about  6  in.  long 
soldered  to  each,  and  each' liaving  a  small  hole  drilled 


Fig.  91. — Armature,  showing  |-in.  Limit. 

at  one  end  to  take  a  small  wood  screw,  as  shown  in 
Fig.  92. 

The  commutator  should  be  in  two  parts,  arranged 
BO  that  the  brushes  work  on  one  face,  and   not  on 


Fig.  92.— Shape  of 
Brush. 


Fig.  93.— Face  of 
Commutator. 


the  rim.  This  plan  has  been  adopted  ^  as  the  motor  is 
designed  to  be  made  without  using  a  lathe,  and  to 
true  up  a  round  surface  is  next  to  impossible  without 
a  lathe. 

For  the  body  of  the  commutator  take  a  cylindrical 
piece  of  hird  wood  not  less  than  f  in.  diameter,  and 


ELECTRIC  MOTORS  WITHOUT  CASTINGS.     103 

cut  off  £  in.  of  it  quite  square.  A  piece  of  an  old 
round  ruler  does  very  well  indeed ;  true  up  both  flat 
faces,  and  carefully  drill  a  hole  through  the  exact 
centre  large  enough  to  fit  tightly  on  a  thick  knitting- 
needle,  2£  in.  of  which  will  make  a  very  good  steel 
shaft. 

From  sheet  copper  cut  a  disc  of  the  same  size  as 
the  wooden  body,  and  fasten  it  on  the  wood  with 
four  small  wood  screws,  and  counter-sink  them  as 


Fig.  94.— Armature  Shaft  complete. 


shown  in  Fig.  93.  Cut  the  copper  right  through  the 
centre  with  a  file,  and  saw  down  through  the  wood  for 
about  \  in ;  the  thickness  of  a  small  saw-cut  will  be 
quite  wide  enough  for  the  slits. 

Having  gone  so  far,  take  off  the  two  pieces  of  copper, 
mark  them  so  that  they  can  be  put  on  again  in  the 
same  positions,  and  cut  a  notch  in  the  middle  of  each 
as  in  Fig.  93,  to  prevent  any  chance  of  contact  with  the 
shaft ;  screw  them  on  again,  and  glue  into  each  side  of 
the  slot  two  little  pieces  of  boxwood  or  bone,  so  that 
they  stand  just  above  the  copper.  Then  file  up 
the  whole  face,  bone  strips,  and  screw-heads  to  a  true 
and  even  smooth  face,  square  with  the  shaft-hole. 

Make  the  yoke  for  the  armature  from  sheet  brasa 
about  ^  in.  thick.  Cut  a  piece  about  If  in.  long  and 
J  in.  wide,  and  bend  it  as  shown  to  the  right  in  Fig.  94,  so 


104        DYNAMOS  AND  ELECTRIC  MOTORS. 

that  it  will  touch  the  ends  of  the  armature  and  enclose 
the  coils.  It  may  perhaps  be  necessary  to  cut  it  a 
little  longer  than  If  in. ;  all  depends  on  how  much 
wire  has  been  wound  on  the  armature. 

In  the  centre  of  this  yoke  drill  a  hole  to  fit  the 
bit  of  knitting-needle  which  forms  the  shaft ;  then 
carefully  adjust  the  yoke  on  the  armature  so  that  the 
hole  for  the  shaft  comes  exactly  in  the  centre  of  the 
armature  and  coils ;  fasten  both  together  with  twine  to 
prevent  any  chance  of  shifting,  and  solder  the  two 
ends  of  the  yoke  to  the  two  ends  of  the  armature. 

Now  place  the  steel  shaft  through  the  hole  in  the 
yoke,  see  that  it  is  perfectly  perpendicular  to  the 


Fig.  95.— End  View  of  Brass  Bearing  for  Armature  Shaft. 

face  of  the  armature,  and  solder  it  in,  taking  care  not 
to  drop  any  hot  solder  upon  the  armature  coils.  As 
there  will  not  be  much  chance  of  truing  up  afterwards, 
try  to  get  everything  square  when  fixing  in  the  shaft. 

The  shaft  bearings  are  four  pieces  of  brass  cut  from 
the  same  piece  as  the  yoke,  or  from  sheet  brass  a  little 
thicker ;  two  measure  about  1£  in.  by  T\  in.,  and  two 
about  £  in.  by  -^  in.  They  are  each  drilled,  as  shown 
in  Figs.  94  and  95,  to  take  four  small  wood  screws  and 
the  shaft.  The  best  way  to  drill  the  shaft-hole,  shown 
in  the  centre  of  Fig.  95,  is  to  fix  both  pairs  of  brasses 
to  any  spare  piece  of  wood  side  by  side,  just  in  the 
position  they  will  occupy  on  the  frame,  only  close  to- 
gether, and  carefully  drill  right  through  both  at  once, 
square  and  true.  Before  taking  them  off  mark  them 
all,  to  ensure  getting  them  back  in  their  places  when 
they  are  to  be  fixed. 

The  [stand  and  blocks  can  be  made  of  any  kind  of 
hard  wood  preferred.  Their  form  does  not  matter  much, 
so  long  as  the  one  at  the  top  of  the  field  magnet  is  made 
as  shown  in  Figs.  88,  89,  and  90. 

The  block  for  the  bearings  and  shaft  can  be  a  simple 


ELECTRIC  MOTORS  WITHOUT  CASTINGS.     105 

cube ;  only  both  blocks  must  be  of  such  a  height  as  to 
bring  the  centre  line  of  the  shaft  on  a  level  with  the  centre 
line  of  the  field  magnet  ends.  The  blocks  can  be  glued 
on  the  stand  after  their  positions  have  been  determined, 
or  fastened  by  screws  through  the  bottom  of  the  stand, 
or  they  may  be  fixed  in  both  ways.  Four  little  binding- 
screws  will  be  wanted  for  the  stand,  as  in  Fig.  87  (p.  98), 
which  is  a  sketch  of  the  model  in  its  simplest  form 
complete,  but  not  drawn  to  scale. 

When  fixing,  the  commutator,  with  its  copper  face 
outwards,  can  be  slipped  on  the  shaft  right  up  to  the 
yoke,  the  slits  being  parallel  with  the  length  of  the 
armature.  A  little  strong  glue  dropped  on  each  side, 
between  the  yoke  and  the  wooden  back  of  the  com- 
mutator, will  hold  them  together  quite  tight  enough, 
especially  if  the  shaft-hole  is  not  large. 

Now  bring  out  the  ends  of  the  coil,  one  to  each  side 
of  the  yoke ;  cut  them  just  long  enough  to  reach  the 
edge  of  the  copper  face  of  the  commutator,  but  not  to 
press  against  the  yoke  ;  bare  the  ends,  and  solder  one  to 
each  segment  of  the  rim,  taking  care  that  no  solder  runs 
on  up  the  copper  face. 

Cut  a  small  disc  of  stout  lead  A,  solder  this 
on  the  end  of  the  shaft  in  such  a  place  that  it  balances 
the  armature,  commutator,  etc.,  and  put  it  on  true  to 
prevent  any  wobbling.  This  little  disc  has  two  uses : 
it  makes  the  model  run  easier  by  means  of  its  balancing 
power,  and  it  helps  the  armature  over  the  two  dead 
points. 

The  magnet  may  now  be  screwed  tight  on  its  seat, 
silk  ribbon  having  been  previously  wound  round  the  coils 
to  prevent  the  wood  cutting  them.  The  brass  bearings 
can  then  be  put  on  the  other  block  in  their  proper  places, 
the  one  farthest  from  the  magnets  being  flush  with  the 
side  of  the  block,  so  that  a  little  brass  washer  can  work 
against  it.  This  washer  must  be  soldered  on  the  shaft 
as  shown  at  B  in  Fig.  94,  where  A  is  a  lead  disc,  c  o 
the  bearings,  D  the  brush,  E  the  commutator,  v  the 
yoke,  and  a  the  armature. 


io6 


DYNAMOS  AND  ELECTRIC  MOTORS. 


Put  on  the  shaft,  and  fasten  up  the  bearings. 
Slack  the  button  of  the  field  magnet,  and  adjust 
it  so  that  the  armature  will  run  freely,  as  near  as 
possible  to  the  end  of  the  magnet  without  any  chance  of 
touching.  Fasten  on  the  brushes,  one  on  each  side  of  the 
shaft,  and  between  the  bearings ;  mind  they  touch 
nothing  but  the  wood.  Set  the  armature  opposite  the 
ends  of  the  magnet,  and  bend  the  brushes  so  that  they 
each  press  gently  on  the  commutator.  The  dotted  lines 


Fig.  96.— End  Elevation.  Fig.  97.— Side  Elevation. 

Figs.  96  and  97.— Miniature  Electric  Motor  with  Iron  Yoke. 

in  Figs.  93  and  94  (pp.  102  and  103),  show  a  position  for 
the  brushes,  but  their  best  place  will  be  found  after 
the  model  has  been  set  going. 

Now  bring  the  ends  of  the  wires  from  the  brushes  to 
the  two  first  binding-screws,  and  the  two  ends  of  the 
field  magnet  coil  to  the  other  two.  Let  us  number  the 
four  binding-screws  from  1  to  4,  Nos.  1  and  2  being  con* 
nected  to  the  two  fore  ends  of  the  field  magnets,  and 
Nos.  3  and  4  to  the  two  brushes.  By  connecting 
one  pole  of  a  battery  to  Nos.  1  and  3,  and  the 
other  pole  to  Nos.  2  and  4,  the  armature  and  fields 
will  be  in  parallel.  In  other  words,  if  it  were  a 
dynamo,  with  a  lamp  where  the  battery  is  in  the 
circuit,  it  would  be  said  to  be  a  shunt  machine. 
If  now,  with  a  short  length  of  spare  wire,  Nos.  2 
and  3  be  joined,  and  one  pole  of  the  battery  con- 
nected to  No.  1,  and  the  other  to  No.  4,  the  armature 
and  fields  will  be  in  series.  Also  by  connecting  Nos.  1 


ELECTRIC  MOTORS  WITHOUT  CASTINGS.     107 

and  4  with  a  spare  piece  of  wire,  and  the  battery  to 
Nos.  2  and  3,  they  will  still  be  in  series,  but  the  current, 
not  the  motor,  will  be  reversed— that  is,  if  you  have  not 
turned  the  battery  round,  or  placed  the  pole  that  was  in 
No.  1  into  No.  2,  and  the  same  the  other  side.  Another 
way  is  to  connect  one  cell  to  Nos.  1  and  2,  and  another 
cell  to  Nos.  3  and  4,  then  reverse  the  current  in  either 
Nos.  1  and  2,  or  Nos.  3  and  4,  and  the  motor  will  be 
reversed. 

Anyone  who  follows  the  foregoing  instructions  with 
a  little  care  may  have  a  small  model  electric  motor  at  a 


U 


Fig.  98.— Side  Elevation. 


Fig.  99.— End  Elevation. 


Fijjs.  98  and  99.— Small  Motor,  with  Horse-shoe  Magnet 
and  Wooden  Saddle. 

merely  nominal  cost,  the  only  expense  being  the  copper 
wire,  four  small  binding-screws,  and  some  small  wood 
screws ;  almost  any  kind  of  close-grained  wood  can  be 
used  for  the  stand.  All  the  rest  of  the  stuff,  such  as  the 
iron,  odd  bits  of  copper,  brass,  etc.,  might  be  got  from 
an  old  scrap-heap. 

Two  other  small  motors  are  shown  in  Figs.  96  to  106. 
A  fair-sized  motor  of  this  type,  with  a  fly-wheel  about 
lj  in.  in  diameter,  will  be  found  very  handy  to  revolve 
small  Geissler  tubes,  or  to  work  small  models.  In  the 
motor  here  described,  the  balance-wheel  of  a  small  round 
American  clock  was  used  for  a  fly-wheel,  which  is  about 
f  in.  in  diameter.  The  drawings  are  all  in  proportion, 
so  that  a  scale  can  be  made,  which  will  serve  to  work 
from. 


io8        DYNAMOS  AND  ELECTRIC  MOTORS. 


Figs.  96  and  97  (p.  106),  show  an  end  and  side  eleva- 
tion of  the  motor,  with  a  small  angle  iron  for  a  yoke,  into 
which  the  magnet  cores  are  either  screwed  or  bolted. 
This  method,  of  course,  is  the  neatest,  and  will  look  the 
best ;  but  as  it  necessitates  the  use  of  a  few  extra  tools, 
nothing  more  will  be  mentioned  about  it,  the  drawings 
speaking  for  themselves.  The  simpler  form,  shown 
complete  by  Figs.  98,  99,  and  100,  will  be  followed  ; 
here  a  piece  cf  round  bent  iron  serves  for  a  magnet,  held 
in  its  place  by  a  small  wooden  saddle  and  a  button. 
In  fact,  the  whole  motor  given  in  these  three  figures 
can  be  made  from  a  few  scraps  of  iron,  brass,  and  wood. 


Fig.  100.— Plan  of  Small 
Motor. 


Fig.  101.— Bearing 
Brackets. 


A  piece  of  soft  iron  wire,  \  in.  in  diameter,  will  make 
the  magnet,  bent  to  the  form  and  proportions  given  in 
Fig.  103  (p.  110).  Two  little  brown-paper  bobbins,  with 
very  thin  wooden  ends,  will  be  required,  as  in  Fig.  102  ; 
fill  these  with  No.  26  s.w.o.  or  No.  28  S.W.G.  silk- 
covered  copper  wire.  It  does  not  matter  at  which  end 
of  the  bobbins  the  wire  ends  come  out  as  long  as  they 
are  connected  one  with  the  other. 

To  connect  the  coils  of  the  magnet,  one  end— it 
matters  not  which— will  have  to  go  direct  to  one  of  the 
binding-screws,  and  be  clamped  under  it,  while  the 
other  end  has  to  be  clamped  under  the  foot  of  the  back 
bearing  bracket.  The  wire  from  the  other  binding-screw 
goes  to  the  foot  of  the  break  spring  (see  Figs.  98  to  100). 

Having  made  a  little  stand  of  polished  or  varnished 


ELECTRIC  MOTORS  WITHOUT  CASTINGS.     109 

wood,  fix  a  small  block  at  one  end  and  clamp  in  the 
magnet  and  bobbins  by  means  of  a  wood  screw  and  a 
wooden  button.  Figs.  98  and  100  show  this  part  of  the 
fitting.  The  bearing  brackets  (Fig.  101)  are  cut  out  of 
sheet  brass.  The  back  one,  between  the  bobbins  of  the 
magnet,  has  a  small  hole  drilled  half  through  it;  the  other 
carries  a  small  screw  with  a  hole  drilled  at  its  end  ;  the 
two  form  point  bearings  for  the  fly-wheel  spindle.  These 
brackets  should  be  fastened  to  the  stand,  so  that  the  cross 
armature  may  revolve  as  close  as  possible  to  the  poles 
of  the  electro- magnet  without  touching  it  (see  Figs.  98 


Fig.  102.— Bobbin  for  Magnet  Coila. 

to  100).  Two  small  binding-screws  are  fixed  to  the 
side  of  the  stand  (see  Figs.  98  to  100) ;  one  end  of  the 
coil  on  the  bobbins  is  fixed  under  one  binding-screw, 
and  the  other  end  of  the  coil  is  fixed  under  the  back 
bracket  bearing. 

The  most  delicate  part  of  this  model  is  the  contact 
spring,  and  as  the  machine  is  so  small  the  pressure  of 
this  spring  must  be  very  slight  indeed,  although  making 
good  contact  when  required.  One  of  the  best  methods 
of  making  this  spring  is  to  take  a  length  of  No.  24  s.w.G. 
or  No.  22  S.W.G.  silk-covered  copper  wire  and  bare  about 
i  in.  at  one  end  ;  beat  this  out  with  a  hammer,  almost 
as  thin  as  copper  foil,  cut  the  tip  square,  coil  up  the  rest 
of  the  wire  to  form  a  spiral,  and  slip  it  loosely  over  a 
small  wooden  peg  in  the  stand  (see  Figs.  98  to  100), 
fixing  the  bottom  of  the  spring  to  the  stand  by  means  of 
a  small  spot  of  glue.  The  little  flattened  tip  must  be 
bent  with  a  pair  of  pliers,  so  that  it  will  just  touch  the 
tips  of  the  teeth  on  the  contact  breaker,  leaving  them 
free  whenever  the  arms  of  the  armature  are  exactly 
opposite  the  poles  of  the  magnet.  The  other  end  of  this 
contact  spring  goes  under  the  other  binding-screw.  All 


no         DYNAMOS  AND  ELECTRIC  MOTORS. 

ends  of  wire  are,  of  course,  scraped  clean  and  bright  just 
before  being  clamped  under  binding-screws,  etc. 

The  small  armature  is  made  of  soft  wrought  iron, 
about  T\  in.  thick,  and  must  be  cut  to  the  shape  shown 
in  Fig.  104.  File  and  trim  it  up  true,  and  drill  a  hole 


Fig.  103. — Horse-shoe 
Magnet. 


u 

Fig.  104.— Iron 
Armature. 


through  its  centre  to  take  the  spindle  or  shaft.  Tin 
the  tips  of  the  arms  on  one  side  ;  then,  with  a  small 
copper  bit,  solder  the  tips  to  the  rim  of  the  balance- 
wheel. 

The  contact  breaker  for  this  size  of  motor  should 


Fig.  105.— Setting-out 
Contact  Breaker. 


Fig.  10G.— Fly-wheel  Arma- 
ture and  Contact  Breaker. 


be  about  \  in.  in  diameter  when  finished.  It  is  made 
from  sheet  brass,  T*  in.  thick.  Fig.  105  shoAvs  the 
method  of  setting  out  the  four  teeth,  which  can  be  cut 
with  a  small  file.  A  hole  must  be  carefully  drilled 
through  the  centre  and  the  contact  breaker  soldered  to 
the  shaft  of  the  fly-wheel,  as  shown  in  Fig.  106,  on  the 
side  opposite  to  the  armature.  After  trimming  all  up, 
this  completes  the  fly-wheel. 

It  is  not  necessary  to  describe  how  to  make  such 
small  binding-screws  as  will  be  required;  dealers  sell 
them  for  about  l£d.  each. 


ELECTRIC  MOTORS  WITHOUT  CASTINGS,     in 

The  model  works  by  the  current  entering  at  one 
binding-screw,  going  round  the  coils  of  wire  and 
making  the  core  a  magnet,  which  then  attracts  its 
armature.  At  the  moment  the  armature  is  opposite 
the  poles,  the  current  is  broken  by  the  spring  leaving  a 
tooth  on  the  contact  breaker ;  the  core  immediately 
ceases  to  be  magnetic,  and  allows  the  armature  to 
proceed  by  the  impetus  given  to  the  fly-wheel  it  is 
fastened  to  till  the  spring  touches  the  next  tooth,  and 
so  on. 

A  small  dry  cell  will  be  the  most  convenient  for 
driving  the  little  model.  One  pole  of  the  cell  must  be 
connected  to  one  binding-screw,  and  the  other  pole  to  the 
other  binding-screw.  A  small  switch  can  be  added  to 
cut  ofl  the  current  and  stop  the  motor ;  otherwise,  one 
wire  must  be  1  disconnected  from  one  of  the  binding- 
screws. 

A  half -pint  bichromate  cell  also  will  drive  the  little 
motor  well,  and  for  one  charge  from  six  to  eight 
hours'  work  can  be  taken  from  it,  either  at  odd  times 
or  at  one  run 

When  the  model  is  complete,  for  appearance 
sake  it  should  be  neatly  painted  with  red  sealing- 
wax  varnish,  black  paint,  or  Brunswick  black. 
Sealing-wax  varnish  is  used  so  much  for  electrical 
models,  etc.,  on  account  of  its  insulating  properties, 
which  are  far  above  ordinary  oil  paints.  The  coils  need 
not  be  painted ;  and  unless  special  wire  is  bought,  the 
silk  on  it  will  be  green.  Keeping  all  brass  bright 
and  showing  the  coils  of  green  silk-covered  wire  will 
give  a  very  pretty  appearance  to  the  model,  which 
when  made  very  small,  is  a  taking  little  novelty. 


XI2 


CHAPTER  IX. 

HOW  TO  DETERMINE  THE  DIRECTION  OF  ROTATION  O? 
A  MOTOR. 

IN  dealing  with  some  of  the  principles  on  which  electric 
motors  act,  we  will  take  as  an  example  the  Siemens  H. 
girder  type.  This  form  of  motor  has  been  chosen  partly 
because  of  its  simplicity  of  construction,  partly  as  it  is 
such  a  favourite  form  for  small  motors.  In  this  chapter 
an  endeavour  will  be  made  to  make  the  principles  clear 
by  illustrating  some  of  the  laws  that  govern  this  type 
of  machine,  without  in  any  way  going  into  the  subject 
of  construction. 

The  principal  law  to  understand  is  that  governing 
what  happens  when  a  length  of  covered  copper  wire  is 
wound  round  a  bar  of  soft  iron,  and  an  electric  current 
is  passed  through  the  wire.  It  is,  of  course,  well  known 
that  the  iron  becomes  a  magnet,  and  remains  a  magnet 
as  long  as  the  current  flows  ;  but  there  are  other  laws  of 
great  importance  to  be  considered. 

Take  a  small  bar  of  iron,  as  N  s  in  Fig.  107  ;  hold  the 
end  N  in  your  left  hand,  and  wind  a  length  of  covered 
copper  wire  upon  the  iron,  beginning  from  your  left 
hand  and  proceeding  towards  the  other  end,  describing 
circles  with  your  right  hand  in  the  same  direction  as 
the  hands  of  a  clock  turn — that  is,  away  from  you  on 
top  of  the  iron,  and  towards  you  underneath.  If  you 
now  pass  an  electric  current  through  the  wire  coil,  from 
the  left-hand  end  to  the  right-hand  end,  as  shown  by 
the  arrows — that  is,  if  you  connect  the  carbon  plate 
of  an  active  battery  to  the  left  hand,  and  the  zinc  plate 
to  the  right — the  left-hand  end  of  the  iron  becomes  the 
north  pole  of  a  magnet,  and  the  end  that  is  at  your 
right  hand  becomes  the  south  pole. 


DIRECTION  OF  ROTATION  OF  A  MOTOR.    113 

Now  take  the  iron  bar,  but  wind  it  in  the  reverse 
way  —  that  is,  as  you  wind  on  the  wire  describe  circles 
with  your  right  hand  in  a  direction  contrary  to  that 
taken  by  the  hands  of  a  clock,  as  in  Fig.  108  —  that  is, 
pass  the  wire  from  you  when  going  under  the  iron,  aud 
bring  it  towards  you  when  coming  over  the  top.  Then 
send  the  current,  as  before,  in  at  the  left-hand  end  and 
out  at  the  right,  as  shown  by  the  arrows,  and  the  poles 


sr/y  /  / 


£|H 


Fig.  109. 


\ 


Nl\\\\\k 
jj  V   V    v    V    v  ' 


Fig.  110. 

Figs.   107   to  110.— Directions  of   Currents   and  Resultant 
Magnetism  in  Bar  Magnets. 

will  be  reversed— that  is,  the  north  pole  will  be  towards 
the  right  hand,  N,  and  the  south  pole  to  the  left,  s. 

Fig.  109  is  wound  in  the  same  direction  as  Fig.  107, 
but  the  current  flows,  as  shown  by  the  arrows,  from  the 
right  hand  to  the  left ;  this  will  cause  the  poles  to  be 
reversed.  Fig.  110  is  wound  in  the  same  direction  as 
Fig.  108  ;  but  by  reversing  the  direction  of  the  current, 
as  shown  by  the  arrows,  the  poles  again  become  reversed, 
as  occurred  in  the  other  case.  This  is  what  happens  in 
a  shuttle  armature  when  the  brushes  cross  the  insulating 
strips  of  the  commutator  :  the  direction  of  magnetism 
set  up  in  the  armature  by  the  armature  current  is 
reversed  by  the  current  being  reversed. 

A  very  good  way  to  master  this  rule  is  to  get  a  piece 
of  wood,  and  mark  one  end  "S"  and  the  other  end 
"  N."  Then  get  a  piece  of  string;  on  one  end  tie  a  label, 
ft 


ii4        DYNAMOS  AND  ELECTRIC  MOTORS. 


marked  "  +,"  or  positive,  on  the  other  end  tie  another 
label  marked  "  — ,"  or  negative.  With  the  stick  and  the 
string  practise  the  foregoing  rule. 

The  next  law  to  be  understood  is  (a)  if  poles  of  the 
same  kind  are  brought  near  each  other,  they  will  repel 
one  another ;  (6)  if  two  different  poles  are  brought  to- 
gether, they  will  attract  one  another — that  is,  north  to 


Fig.  111.  Tl'l'l          Fig.  112. 

Figs.  Ill  and  112. — Series  Motors. 

north,  repulsion  ;  south  to  south,  repulsion  ;  but  north  to 
south,  attraction. 

In  the  diagrams  of  motors  (Figs.  Ill  to  116),  the 
commutators  and  brushes  have  been  left  out  in  order 
to  simplify  the  drawings.  It  must  be  understood  that 
at  the  moment  the  two  poles  of  the  armature  are 
opposite  the  two  poles  of  the  field  magnet,  the  two 
brushes  are  resting  upon  the  insulating  strips  of  the 
commutator  ;  immediately  after  that,  as  the  armature 
rotates,  the  direction  of  the  current  is  changed  through 
the  armature  and  its  poles  reversed.  Though  this  is 
not  the  exact  fact  in  practice,  in  this  case  we  may 
assume  it  to  be  so. 

In  a  motor  of  the  Siemens  type  driven  in  series,  the 
current  passes  either  first  round  the  magnets,  then 


DIRECTION  OF  ROTATION  OF  A  MOTOR.    115 

through  the  armature,  and  back  to  the  batter y,  as  in 
Fig.  Ill,  or  in  the  reverse  direction,  first  through  the 
armature,  then  the  magnets,  and  back  to  the  battery, 
as  in  Fig.  112.  It  may  appear  curious,  but  whichever 
way  a  current  is  sent  through  a  series  motor,  as  shown, 
it  will  rotate  the  same  way. 

Let  us  follow  the  winding  in  Fig.  Ill,  starting 
from  the  battery.  We  will  suppose  that  the  direction  of 
the  current  is  as  shown  by  the  arrows.  The  first  magnet 
core  to  be  reached  is  the  left-hand  one ;  this,  it  will  be 
observed,  is  wound  as  the  iron  bar  in  Figs.  108  and  110, 
and  if  the  foregoing  law  has  been  understood,  it  will 
be  seen  that  a  south  pole  is  left  behind  the  winder. 
Crossing  over  to  the  other  core,  the  winding  is  done 
as  shown  in  Fig.  108,  and  this  produces  a  north  pole 
at  N.  After  this  the  current  goes  to  one  brush,  then 
through  the  commutator  (these  are  not  shown),  and  into 
the  armature,  wound  in  the  same  way  as  the  bar  in 
Fig.  109,  which  produces  a  north  pole  to  the  right  and  a 
south  pole  to  the  left.  After  this,  the  current  again  goes 
through  the  commutator,  through  the  other  brush,  and 
so  returns  to  the  battery. 

The  position  of  the  armature  as  shown  in  Fig. 
Ill  is  a  little  beyond  the  horizontal,  so  that  the 
brushes  are  in  contact  with  the  commutator,  and  the 
current  will  flow  through  the  whole  machine.  Now 
study  what  happens.  The  south  pole  of  the  armature 
is  against  or  near  the  south  pole  of  the  magnet,  and 
the  north  pole  of  the  armature  is  near  the  north  pole 
of  the  magnet.  This  means  mutual  repulsion,  so  the 
armature  takes  the  motion  indicated  by  the  curved 
arrow  above  it,  which,  by  the  way,  shows  the  direction 
of  motion  in  all  the  diagrams.  Influenced  by  repulsion, 
this  motion  continues  until  the  south  pole  of  the  arma- 
ture nears  the  north  pole  of  the  magnet ;  then,  as  they 
are  of  different  poles,  they  will  attract  each  other  until 
the  south  pole  of  the  armature  has  arrived  exactly 
opposite  the  north  pole  of  the  magnet.  At  that  moment 
the  insulating  strips  cross  the  brushes  and  change  the 


n6        DYNAMOS  AND  ELECTRIC  MOTORS. 


poles  of  the  armature,  and  what  was  formerly  the  south 
pole  in  the  armature  now  becomes  its  north  pole,  and 
like  poles  are  again  together  and  mutual  repulsion  is 
set  up,  causing  a  repetition  of  the  same  series  of  motions 
as  has  just  been  described. 

If  the  battery  current  is  now  reversed,  as  shown  in 
Fig.  112  (p.  114),  and  the  winding  is  followed  out,  it  will 
be  found  that  every  pole  has  been  changed,  so  that  again 
we  have  like  poles  to  like,  and  the  motion  becomes  the 


Fig.  113.  Fig.  114. 

Fig.  113  and  114.— Shunt  Motors. 

same  as  in  Fig.  111.  This  means  that  if  a  motor  is 
driven  in  series,  it  will  turn  in  the  same  direction, 
whichever  way  the  current  goes. 

When  a  motor  is  driven  as  a  shunt  machine,  the  current 
from  the  battery  is  divided— part  being  shunted  to  the 
magnets  and  part  to  the  armature.  After  the  divided 
current  has  passed  through  the  machine,  it  again  unites 
in  one  wire  and  returns  to  the  battery.  By  following 
the  windings  and  the  direction  of  the  current  in  Fig.  113, 
it  will  be  seen  that  the  left-hand  limb  s  is  the  same 
as  s  in  Fig.  Ill  (p.  114),  and  that  it  is  a  south  pole; 
the  other  must,  of  course,  be  a  north  pole,  as  the  two 


DIRECTION  OF  ROTATION  OF  A  MOTOR.    117 


limbs  of  the  magnet  are  always  wound  so  as  to  give 
opposite  poles.  Now  follow  out  that  branch  of  the 
current  which  passes  through  the  armature  ;  this  will 
enter  on  the  left-hand  side  and  be  wound  with  a  coil 
going  in  the  direction  shown  in  Fig.  109  (p.  113);  this 
will  give  a  north  pole  to  the  left,  and  a  south  pole  to 
the  right.  The  current  then  goes  through  the  commu- 
tator, etc.,  after  which  it  joins  the  current  round  the 
magnet,  and  so  returns  to  the  battery. 

In  this  case  it  will  be  seen  that  we  have  unlike  poles 


Fig.  115.  Fig.  116. 

Figs.  115  and  116.— Motors  driven  with  Two  Batteries. 

near  each  other ;  these  exert  mutual  attraction,  and  the 
armature  rotates  in  the  direction  opposite  to  that  shown 
in  both  Figs.  Ill  and  112  (p.  114). 

Now  study  what  happens  when  the  shunted  part  of 
the  current  is  reversed  through  the  armature,  and  the 
part  of  the  current  through  the  magnets  is  left  as  it  was. 
Fig.  114  will  show  this.  We  have  like  poles  together, 
exerting  mutual  repulsion,  and  the  motion  of  the  arma- 
ture is  reversed,  turning  in  the  same  direction  as  shown 
in  Figs.  Ill  and  112.  We  should  also  get  a  reversal  by 
reversing  the  current  round  the  magnet  whilst  keeping 


nS        DYNAMOS  AND  ELECTRIC  MOTORS. 

the  current  in  the  armature  in  the  same  direction  as  in 
Fig.  113  (p.  114). 

For  further  study,  suppose  that  the  motor  is  driven 
with  two  batteries,  one  to  excite  the  magnets  and  the 
other  to  excite  the  armature,  as  in  Figs.  115  and  116. 
If  now  the  windings  and  the  direction  of  the  current 
are  followed  out  as  in  all  the  other  cases,  the  direction 
in  which  the  armature  will  move  will  be  seen  readily. 
Here,  as  was  the  case  with  the  shunt  motor,  if  the  current 
is  reversed  in  either  the  magnet  or  the  armature,  the 
direction  in  which  the  motor  turns  will  be  reversed. 

Note  that  all  the  diagrams,  from  Fig.  Ill  to  Fig.  116, 
are  wound  the  same  way  ;  this  has  been  done  to  show 
some  of  the  different  ways  that  one  motor  can  be  driven, 
by  making  different  combinations  with  the  current.  But 
too  much  space  would  be  required  to  show  all  com- 
binations of  winding  and  all  combinations  of  current 
possible.  As  there  are  many  more  combinations  than 
those  shown,  the  reader  will  find  it  useful  to  sketch  out 
a  few  skeleton  diagrams,  and  put  the  windings  and  the 
currents  in  various  ways  different  from  these,  and  work 
out  the  motions  himself. 

As  an  example,  supposing  you  have  just  bought  the 
castings  of  a  small  model  girder-motor,  and  that  you 
wish  to  make  it  turn  the  reverse  way  to  Figs.  1 11  and  112 
(p.  114),  when  driven  in  series.  Wind  the  magnet  as  in 
Figs.  Ill  and  112,  but  wind  the  armature  as  in  Figs.  110 
and  113 ;  or,  on  the  other  hand,  wind  the  armature  as  it 
is  in  Figs.  Ill  and  112,  but  reverse  the  twist  in  the 
magnet.  Then  you  will  have  a  motor  that,  when  driven 
in  series,  will  turn  in  the  reverse  direction  to  that  shown 
in  Figs.  Ill  and-  112.  All  this  is  very  simple — when 
once  the  law  of  winding  a  simple  bar  of  iron  has  been 
mastered,  and  it  is  remembered  that  two  like  poles  repel, 
and  two  unlike  poles  attract  each  other. 

Finally,  it  must  be  said  that  it  is  always  best  to  drive 
a  motor  with  the  current  it  was  intended  to  take,  and  if 
it  is  desired  to  try  experiments  of  this  sort,  rig  up  a 
motor  specially  for  the  purpose. 


CHAPTER  X. 

HOW  TO  MAKE  A  SHUTTLE-AKMATURE  MOTOR. 

THE  small  electro-motor  shown  in  the  accompanying 
illustration  (Fig.  117)  is  suited  to  the  requirements  of 
those  who  have  access  to  a  lathe  for  turning  certain 
parts.  It  is  a  machine  that  will  look  very  well  indeed 


Fig.  117.— Shuttle- Armature  Motor  Complete. 

if  good  workmanship  is  shown  in  the  fitting  and 
finishing  of  the  various  parts.  But  some  careful  fitting 
is  required  to  make  it  run  well.  When  properly 
made,  it  will  drive  a  small  polishing  or  dental  lathe,  or 
a  small  fretwork  machine,  or  a  small  drilling-machine, 
or  even  a  light  sewing-machine,  with  a  battery  power  of 
some  three  or  four  quart  chromic  acid  cells,  or  the 
equivalent  electrical  energy  from  any  other  source. 

The  set  of  castings  required  consists  of  two  malleable 
iron  field  magnet  cores  and  bridges,  as  shown  at  Fig.  118, 
each  measuring  4£  in.  in  length  by  2J  in.  in  width  ;  one 
malleable  iron  casting  (Fig.  119)  for  the  armature, 


120        DYNAMOS  AND  ELECTRIC  MOTORS. 

measuring  Z\  in.  in  length  by  If  in.  in  diameter ;  two 
gun-metal  castings,  1|  in.  in  diameter  (Fig.  120),  for  ends 
of  the  armature ;  two  brass  castings  of  four-legged 
spiders  for  the  bearings  of  the  spindle ;  one  brass  casting 
of  a  pulley,  l\  in.  diameter  by  T9^  in.  thick  ;  one  brass 
casting  of  a  collar,  1  in.  diameter  by  £  in.  thick ;  two 
brass  end-pieces,  2^  in.  by  f  in.  (Fig.  121),  to  form  feet 
for  the  field  magnets ;  one  brass  casting  for  a  brush 
rocker,  2£  in.  in  length  (Fig.  122) ;  two  brass  castings 


Fig.   118.— Field  Magnet  Casting  for  Shuttle-Armature 
Motor. 


of  brush-holders  (Fig.  123) ;  two  brass  castings  of  set 
screws  (Fig.  124) ;  castings  for  the  brass  nuts,  brass  tube 
for  commutator,  and  a  strip  of  phosphor  bronze  for  the 
brushes.  These  having  been  obtained,  we  will  set  about 
fitting  and  finishing  the  various  parts  and  putting  them 
together. 

The  field  magnet  castings,  if  rough,  will  require 
to  be  filed  to  make  them  fit  and  have  a  presentable 
appearance.  All  lumps  should  first  be  filed  down  with 
a  flat  bastard  file.  The  channel  for  the  armature  must 
next  be  smoothed  with  a  half-round  file,  care  being  taken 
not  to  do  more  than  smooth  the  casting.  The  corners 
of  the  cores  should  be  rounded  off,  to  prevent  them 
from  cutting  into  the  insulating  cover  of  the  wire  aa 
this  is  being  wound  o*n.  The  outsides  may  now  be 
smoothed  and  the  ends  trued,  to  make  the  whole  fit  well 


A  SHUTTLE- ARMATURE  MOTOR.  isi 

together.  The  top  casting  for  the  field  magnet  is  usually 
a  little  thicker  than  the  under  one.  The  under  field 
magnet  casting  will  have  the  two  brass  feet  or  holding- 
down  pieces,  shown  at  Fig.  121,  fitted  under  each  end, 
and  must  therefore  have  two  hoies  drilled  at  each  end. 
These  receive  two  small  screws,  which  pass  through  the 


Fig.  119. — Armature  Casting   for  Shuttle-Armature  Motor. 

brass  feet  and  the  lower  casting  into  the  top  casting,  as 
shown  in  Fig.  129  (p.  126).  Small  holes  for  set  screws, 
to  hold  the  feet  of  the  spiders,  must  also  be  drilled  and 
tapped  in  the  corners  of  the  armature  channel,  as  shown 


Fig.  120.— Gun-Metal  Casting  for  Armature  Ends. 

at  Fig.  129  ;  these  are  fitted  with  round-headed  brass 
screws.  Thus  prepared,  the  castings  may  have  a  coat 
of  Japan  black  and  be  set  aside  to  dry. 

The  armature  is  of  the  Siemens  H-girder  type,  in  one 
casting  of  malleable  soft  iron.  This  must  be  filed  smooth 
and  true  at  the  ends,  and  the  channel  must  be  made 
smooth  with  a  file.  The  gun-metal  end-pieces  shown  at 


122         DYNAMOS  AND  ELECTRIC  MOTORS. 

Fig.  120  will  be  fitted  to  the  ends  of  the  armature,  to 
hold  the  steel  spindles.  These  are  made  from  two  2-in. 
lengths  of  £-in.  steel  rod,  turned  true  and  smooth  down 
to  -j8,,-  in.  diam.  Turn  the  end-pieces  smooth,  drill  a 
T\  in.  hole  through  the  boss  of  each,  and  drive  one  end 
of  each  spindle  into  each  boss. 

The  end-pieces  will  be  secured  to  the  ends  of  the 


© 


Fig.  121.— Gun-Metal  Foot  for  Motor. 

armature,  after  being  fitted  true  to  it,  by  small  brass 
screws ;  holes  must  therefore  be  drilled  through  the  end- 
pieces  and  into  the  armature,  which  is  tapped  to  receive 
the  screws.  In  one  of  the  end-pieces  drill  two  extra  holes 
for  the  ends  of  the  armature  coil  to  come  through,  and 
bush  these  holes  with  small  tubes  of  ivory  or  bone.  When 


Fig.  122.— Rocker  for  Brush-Holders. 

the  ends  are  fitted  on,  mount  the  armature  in  a  lathe, 
and  true  it  by  turning  away  just  enough  to  take  off  the 
rough  skin.  This  done,  mark  all  the  screws  and  screw- 
holes  to  correspond,  so  that  they  can  be  identified  when 
the  machine  is  being  put  together.  Take  off  the  ends, 
and  dress  the  web  and  channel  with  shellac  or  good 
sealing-wax  varnish,  then  set  aside  to  dry,  ready  for 
winding. 

Brass   castings    as    shown  at    Fig.    117    fulfil    the 
double  purpose  of  clamps  to  hold  the  field  magnets 


A  SHUTTLE- ARMATURE  MOTOR.  123 

together  and  of  bearings  for  the  armature  spindles. 
These  must  now  be  drilled  to  fit  the  spindles,  with 
holes  in  each  foot  to  receive  the  holding  studs,  and 
with  small  oil  holes  for  each  bearing  ;  then  they  must  be 
filed  smooth  and  neatly  polished.  The  projecting  boss 
of  one  of  these  bearings  must  be  turned  to  form  a 
bearing  for  the  brush  rocker  (Fig.  122),  which  will  fit  on 


Tig.  123.— Casting  for  Brush-Holder. 

like  a  sleeve.     The  insides  of  the  spider  legs  and  bodies 
should  also  be  turned  smooth. 

The  casting  for  the  brush  rocker  is  shown  at  Fig.  122. 
The  hole  in  the  centre  must  be  bored  to  fit  the  boss  on 
the  bearing  above-mentioned ;  and  a  hole  must  be 
drilled  and  tapped  in  the  edge  of  the  rocker  to  receive  a 
set  screw  for  fixing  the  rocker  in  any  required  position. 


Fig.  124.— Casting  for  Milled  Head  Screw. 

Two  rough  brass  castings,  as  shown  at  Fig.  123,  must  be 
turned  and  filed  to  the  form  shown  at  Fig.  125  (p.  124),  to 
form  brush-holders,  and  these  are  held  in  holes,  B  B, drilled 
through  the  ends  of  the  rocker  (Fig  122).  The  holes  in 
the  ends  of  the  rocker  are  drilled  T\  in.  in  diameter, 
and  bushed  with  vulcanite  or  asbestos  board,  with  a 
collar  of  the  same  on  each  side,  to  insulate  the  brush- 
holder  from  the  rocker.  A  fairly  good  bush  can  be 
cut  from  a  piece  of  rubber  tube,  with  two  collars  of  thin 
cloth  to  come  between  the  shoulder  of  the  brush -holder 
and  the  rocker  on  one  side,  and  the  nut  and  the  rocker 
011  the  other ;  but  indiarubber  is  liable  to  be  destroyed 


124        DYNAMOS  AND  ELECTRIC  MOTORS. 

by  oil.  In  Fig.  125  the  part  B  is  first  turned  to  £  in. 
diameter,  and  a  thread  chased  on  it  to  receive  a  brass 
nut.  The  plain  part  to  the  left  of  the  chased  thread 
must  be  drilled  transversely  with  a  -j^-in.  hole,  c,  to 
receive  the  conducting  wire,  and  this  hole  is  met  with 
another,  E,  drilled  from  the  end,  and  tapped  to  receive  a 
binding-screw  with  a  milled  head,  as  shown  at  Fig.  126. 


Fig.  125.— Brush -Holder  Fig.  126.— Screw  with 

complete.  Milled  Head. 

The  other  end  of  the  brush- holder,  D,  is  turned  parallel, 
a  slot  gV  in.  wide  is  cut  up  to  the  shoulder  A,  one  side  of 
the  holder  is  filed  flat,  and  a  ^  in.  hole  is  drilled  through 
both  jaws ;  the  hole  in  one  jaw  is  tapped  to  receive  a 
brass  screw,  which  passes  freely  through  the  other  jaw. 

The    brushes   are    strips    of   phosphor  bronze  foil, 
2  in.  by  ^  in.,  cut  to  the  form  shown  at  Fig.  127.    Six 


Fig.  127.— Brush. 

of  these  strips  soldered  together  at  one  end  form  a  pad. 
A  slot,  \  in.  by  i  in.,  is  cut  through  the  middle  to 
receive  the  adjusting  and  tightening  screw.  There  is  a 
brush-holder  (Fig.  125)  at  each  end  of  the  rocker,  and  in 
the  jaws  of  this  the  brush  is  held. 

A  two-part  commutator,  made  of  a  brass  ferrule  split 
into  two  equal  parts,  will  be  required.  On  this  form  of 
armature  there  is  only  one  coil,  the  two  ends  of  which 
are  connected  to  the  two  parts  of  the  commutator.  The 
brass  tube  which  will  be  suitable  for  the  castings  has  an 
internal  diameter  of  \\  in.  This  is  fitted  on  a  boxwood 
boss  \  in.  in  width,  bored  with  a  hole  which  exactly 


A  SHUTTLE- ARMATURE  MOTOR.  125 

fits  the  spindle  at  that  end  of  the  armature  with 
the  bushed  holes  in  it.  The  ferrule  is  now  to  be 
scribed  into  two  equal  parts,  and  on  each  side  of  the 
dividing  lines  scribe  two  more  lines,  so  as  to  have  the 
three  lines  on  each  side  i  in.  apart.  Through  the  centre 
of  each  of  the  two  side  lines  drill  small  holes  into  the 
boxwood  to  receive  brass  screws,  as  shown  in  Fig.  128. 

Countersink  the  mouths  of  these  eight  holes,  and 
screw  in  the  screws  tight;  then  cut  the  ferrule  into 
two  equal  parts  with  an  oblique  cut,  as  shown 
at  Fig.  128.  This  is  best  done  with  a  hack-saw, 
so  as  to  make  a  clean  cut  through  the  brass  and  into 
the  boxwood_beneath  it.  The  boss,  with  its  split  ferrule, 


Fig.  128. — Commutator. 

is  now  pressed  on  the  spindle  with  the  inner  ends  of  the 
oblique  cuts  adjusted  so  as  to  coincide  with  the  wire 
holes  in  the  armature  ends. 

Winding  the  armature  is  a  simple  matter.  Measure 
off  60  ft.  of  No.  20  S.W.G.  double  cotton-covered  copper 
wire,  roll  it  into  a  hank,  and  soak  it  for  a  quarter  of 
an  hour  in  melted  paraffin  wax,  then  hang  it  up  to  drain 
and  cool.  When  cool,  take  the  armature  in  the  left 
hand,  and  the  wire  in  the  right.  Place  the  commencing 
end  of  the  coil  with  2  in.  left  projecting  at  the  loft  side 
of  the  channel,  and  hold  it  down  with  the  left  thumb 
whilst  the  wire  is  wound  closely  around  the  web  of  the 
armature  in  close  regular  turns,  side  by  side,  to  the  right 
side  of  the  channel,  then  back  again  with  the  same  care 
and  regularity,  until  all  the  wire  has  been  wound  on  in 
regular  and  even  layers.  Then  twist  the  two  ends  to- 
gether to  keep  the  coil  from  unwinding.  Test  each 
layer  for  insulation  as  it  is  wound  on,  and  test  the 
whole  coil  again  when  complete. 


126         DYNAMOS  AND  ELECTRIC  MOTORS. 

The  end-pieces  may  now  be  put  on,  then  the  ends  of 
the  armature  coil  may  be  brought  out  through  the 
bushed  holes  in  the  casting  and  connected  to  the 
commutator.  Each  end  of  the  wire  should  be  soldered 
to  the  inner  edge  of  one  of  the  commutator  pieces,  along 
which  they  may  lie  to  a  length  of  £  in.  The  coil  may 
now  be  given  a  coat  of  sealing-wax  varnish  and  then  set 
aside  to  dry. 

The  field  magnets  must  be  so  wound  as  to  cause  the 
pole  above  the  armature  to  assume  a  magnetism  of 
opposite  polarity  to  that  of  the  pole  below  the  armature. 
It  matters  but  little  whether  a  north  pole  is  at  the 


Fig.  129. — Section  of  Motor  showing  Winding. 

top  and  a  south  pole  at  the  bottom,  or  a  south  pole  at 
the  top  and  a  north  pole  at  the  bottom,  but  they  must 
not  be  both  north  poles  or  both  south  poles.  The  cores 
on  the  two  sides  of  the  arch  must  be  wound  in  opposite 
directions.  Thus,  if  we  wind  the  left-hand  core  of  the 
top  magnet  from  left  to  right  overhanded,  we  must  wind 
the  right-hand  core  from  left  to  right  underhanded. 
In  commencing  to  wind  the  lower  cores  from  the  left- 
hand  side,  we  must  wind  the  left-hand  core  overhanded 
and  the  right-hand  core  underhanded.  This  ensures  a 
south  polarity  to  the  lower  pole,  as  shown  in  Fig.  129, 
if  the  current  is  sent  through  the  wires  in  the  direction 
shown  by  the  arrows. 

Wind  each  core  regularly  with  three  layers  of  No.  20 


A  SHUTTLE-ARMATURE  MOTOR.  127 

S.W.G.  double  cotton- covered  copper  wire,  and  test  each 
layer  for  insulation.  When  the  last  turn  on  each 
core  has  been  reached,  cut  off  the  wire  so  as  to  leave 
6  in.  more  than  is  needed  to  make  the  turn ;  pass 
this  in  under  the  turn  of  wire  so  as  to  form  a  kind 
of  half-hitch,  and  draw  it  tight  to  prevent  the  wire 
from  unwinding  ;  then  give  the  whole  a  dressing  of 
sealing-wax  varnish  to  secure  each  coil  in  its  place, 
and  to  give  the  whole  a  finished  appearance. 

When  the  machine  is  being  put  together,  the  coils 
must  be  connected  as  here  described,  and  shown 
at  Fig.  129.  The  finishing  end  of  the  first  coil  at  A 
must  be  bared  of  the  cotton  covering  and  cleaned  ; 
so  also  must  the  commencing  end  of  the  second  coil 
on  the  next  core  at  B.  Dip  both  cleaned  ends  into 
some  soldering  fluid,  tin  them  with  a  hot  soldering-bit, 
twist  the  tinned  ends  together  with  a  pair  of  pliers,  then 
give  them  a  final  touch  with  the  soldering-bit  to  fuse  the 
solder  and  unite  them.  Each  end  must  be  thus  treated 
and  connected,  namely,  A  to  B,  c  to  D,  and  E  to  F.  The 
two  ends  c  D  may  be  passed  down  holes  made  in  the 
base  of  the  motor,  and  connected  beneath.  The  two 
free  ends  above  the  upper  pole  will  then  go,  one  to  one  of 
the  brushes,  and  the  other  to  one  of  the  terminal  binding- 
screws  on  the  base,  if  the  coils  are  to  be  connected  in 
series  with  the  armature ;  or  both  will  be  connected  to 
the  brushes  if  the  coils  are  to  be  connected  in  parallel 
with  the  coil  on  the  armature,  so  as  to  make  a  shunt 
motor. 

When  fitting  the  parts  together,  the  field  magnets 
may  be  fitted  first,  the  ends  of  the  coils  soldered  and 
tucked  in  out  of  sight,  the  screws  holding  the  two  cores 
inserted  and  screwed  tight,  and  the  brass  feet  screwed 
on.  Next,  fit  the  already  turned  and  polished  spider- 
bearing  to  the  end  opposite  to  that  on  which  the  com- 
mutator is  fixed.  Then  put  in  the  armature,  slip  the 
other  bearing  on  its  spindle,  and  screw  this  bearing  in 
its  place.  Now  turn  the  armature  round  by  hand, 
and  see  that  it  runs  truly  in  the  tunnel,  not  touching 


128        DYNAMOS  AND  ELECTRIC  MOTORS. 

anywhere,  but  equidistant  from  the  sides  at  all  parts. 
The  back  pulley  (see  Fig.  117,  p.  119)  should  now  be 
fitted  on  the  spindle,  and  tightened  on  it  by  means 
of  a  small  set  screw  passing  through  the  boss  on  the 
outside.  The  rocker  may  next  be  fitted  on,  and  se- 
cured to  the  outside  of  the  bearing  by  a  small  set 
screw.  One  of  the  brushes  will  have  its  free  end  bearing 
on  the  top  of  the  commutator,  and  the  other  brush  will 
press  lightly  against  the  under-side  of  the  commutator. 

The  brushes  B,  brush-holders  H,  and  rocker  R.  complete, 
are  shown  in  Fig.  130.    The  exact  position  of  the  brushes 


Fig.  130. — Brush-Holders,  Rocker,  and  Brushes  complete. 

will  be  determined  by  the  direction  of  rotation  of  the  arma- 
ture, the  commutator  running  away  from  the  brushes.  The 
correct  angle  to  set  these  must  be  found  by  experiment. 
The  rocker  can  easily  be  moved  until  the  best  effect  has 
been  obtained,  then  fixed  in  this  position  by  the  set 
screw.  The  collar  is  now  slipped  on  the  spindle,  the 
armature  brought  forward  until  it  runs  free  in  its  proper 
position,  and  the  collar  tightened  to  prevent  undue  end 
shake  of  the  spindle  in  its  bearings.  A  little  end  play 
or  shake  is  always  admissible,  but  side  shake,  due  to 
loose  fitting  in  the  bearings,  must  never  be  allowed. 
The  motor  may  now  be  mounted  on  a  base  made 
of  oak,  teak,  or  mahogany,  and  furnished  with  brass 
terminals  to  the  wire  coils,  as  shown  at  Fig.  117  (p.  119). 
The  insulation  of  the  wires  on  the  field  and  armature 
may  be  tested  in  the  manner  described  in  Chapter  VII. 


I29 


CHAPTER   XI 

UKTY-WATT   UNDEETYPE  DYNAMO   AND   MOTOR. 

The  following  figures  show  a  dynamo  which  will  cither 
light  three  10-volt  5-candle-power  lamps,  or  work  well 
as  a  motor  when  supplied  with  current  from  a  battery. 
The  illustrations  are  all  to  a  scale  of  one-half  full 
size,  and  dimensions  may  be  measured  from  them. 
Assuming  that  the  castings  and  other  materials  are 
leady,  it  will  be  convenient  to  consider  the  work  of 
construction  in  three  divisions — first,  mechanical  con- 
struction ;  second,  insulation  ;  third,  winding  on  the 
wire  and  connecting  up. 

Commence  with  fitting  up  the  brackets  and  armature  ; 
the  holes  for  the  shaft  must  be  drilled  on  the  bearings 
A,  A,  Figs.  131  and  132  (pp.  132  and  133);  at  each  end  of 
the  boss,  punch  a  centre  in  the  middle  of  the  round  part  of 
the  top  of  the  bearing.  The  hole  should  be  drilled  rather 
less  than  £in.  diameter,  a  little  way  in  from  one  end 
first,  then  reverse  the  bearing,  and  drill  up  a  little  from 
the  other  end,  reverse  again,  and  so  on  until  the  holes 
meet  at  about  the  middle.  The  oil  cups  B,  B,  Fig.  132, 
can  be  ditlled  as  shown,  the  hole  at  the  bottom,  about 
^a  in.  diameter,  being  drilled  through  into  the  bearing- 
hole  to  allow  oil  to  pass.  Drilled  thus,  the  holes  for 
the  bearing  will  be  found  to  be  somewhat  rough  and 
perhaps  not  exactly  in  line ;  this  will  be  remedied  by 
a  reamer  or  rose-bit  passed  carefully  through.  Use 
a  little  oil  as  lubricant,  and  work  from  one  end  only. 
If  the  drilling  has  been  carefully  done  with  a  drill  about 
s1^  in.  less  than  the  finished  size  the  hole  will  be  reamed 
quite  smooth.  Care  must  be  taken  not  to  spoil  the 
bearing  surfaces  when  handling  the  castings  for  other 
operations. 
I 


130        DYNAMOS  AND  ELECTRIC  MOTORS. 

The  bore  of  the  field-magnet  casting,  Figs.  133 
and  136,  if  well  cast  will  be  very  nearly  a  true  circle ;  it 
should  be  cleaned  out  with  a  file  to  remove  any  lumps 
or  irregularities.  To  take  a  cut  through  with  a  boring 
bar  on  the  lathe  makes  the  best  job,  but  good  results  may 
be  obtained  without  this  if  a  good  casting  is  secured. 
To  get  the  bearings  in  alignment  a  dummy  armature 
and  shaft  must  now  be  made.  Get  a  piece  of  iron  or 
steel  rod  just  the  length  of  the  armature  shaft  and  of 
a  convenient  diameter,  such  as  f  in.,  and  on  this  mount 
tightly  a  piece  of  hard  wood,  about  If  in.  diameter,  of 
the  length  the  armature  core  will  be,  and  in  the  same 
position.  Turn  the  wood  to  fit  tightly  in  the  bore  of 
field-magnet,  and  turn  the  rod  also  at  each  end  to  fit 
the  bearings.  Place  the  dummy  tight  in  the  bore, 
slip  the  bearing  castings  on  the  spindle,  and  fit  the 
end  lugs  D,  Fig.  132,  to  bed  flat  on  the  sides  of  the 
field-magnet ;  if  they  are  much  out,  the  castings  may  be 
hammered  until  they  are  somewhere  near  right,  and  the 
final  adjustment  effected  with  the  file.  A  little  red 
ochre  mixed  with  oil  and  smeared  on  the  magnet  will 
show  where  the  lugs  touch.  It  is  important  that  these 
brackets  should  bed  properly,  or  they  will  not  be  in 
line  when  screwed  in  place,  and  the  shaft  will  run  stiffly. 

The  holes  for  the  screws  E,  Figs.  132  and  133,  may  be 
drilled  in  the  bearing  castings ;  then  slip  the  bearings  on 
the  dummy  shaft  and  mark  the  field-magnet  by  drawing 
the  point  of  a  scriber  round  the  holes  in  the  castings. 
Some  chalk  rubbed  on  the  magnet  where  the  bearings 
come  will  assist  to  show  the  line.  Tapping  holes  for 
^-in.  screws  may  be  drilled  about  |  in.  deep  in  the 
centres  of  the  marked  circles.  Mark  off  holes  in  the 
field  magnet  feet  for  the  holding-down  screws,  the  posi- 
tions being  taken  from  the  drawing  (see  F,  Fig.  131).  The 
diameter  of  the  holes  may  be  about  ^  in.,  chamfered 
to  suit  the  wood  screws  intended  to  be  used. 

The  armature,  Figs.  134  and  135,  is  now  to  be  made  ; 
its  shaft  is  of  steel  7f  in.  long  ;  if  made  from  rod  that  is 
quite  straight  and  true,  the  diameter  can  be  /„  in.,  so 


UNDERTYPE  DYNAMO  AND  MOTOR.        131 

that  the  central  portion  need  not  be  turned;  but  it 
is  better  to  have  the  diameter  f  in.,  and  take  a  lighl 
cut  all  along,  reducing  to  •&  in.  diameter.  At  th« 
pulley  end  a  length  of  \\  in.  has  to  be  turned  down  to 
form  the  bearing,  and  at  the  commutator  end  a  length  of 
1\  in.  These  necks  should  be  left  a  little  large,  so  that 
they  can  be  fitted  in  after  the  core  discs  H,  Fig.  135 
(p.  138),  are  tightened  up  in  place,  the  screwing  up  of  the 
clamping  nuts  J  having  a  tendency  to  bend  the  shaft. 
The  screwed  portions  for  the  clamping  nuts  are  cut  as 
shown,  for  about  \  in.  at  each  end  ;  a  screw  with  about 
twenty  threads  to  the  inch  is  necessary,  and  is  best  cut 
on  a  screw-cutting  lathe ;  but  if  this  is  not  available,  the 
thread  may  be  started  with  stock  and  dies  and  finished 
with  a  comb  chaser. 

About  120  core  discs,  about  ^  in.  thick,  must  now  be 
prepared.  The  central  holes  must  pass  over  the  shaft 
easily  ;  any  burrs  must  be  filed  off,  for  if  not  flat  the 
screwing-up  of  the  nuts  will  cause  uneven  parts  to 
bend  the  shaft.  In  the  middle  of  the  core  is  the  circular 
groove  K,  Fig.  134,  \  in.  long,  to  take  the  binding  cord. 
To  make  this,  a  few  discs  should  be  reduced  in  diameter 
and  put  on  the  shaft  when  half  the  other  discs  are  on. 
It  is  a  difficult  job  to  turn  out  this  groove  on  the  lathe 
if  left  till  the  core  is  complete.  Before  threading  the 
discs  on  the  shaft  one  side  of  each  should  be  painted 
with  a  thin  coat  of  enamel  or  Brunswick  black  and  left 
to  dry.  The  clamping  nuts  J,  Fig.  134  (p.  138),  are 
circular  pieces  of  brass  f  in.  diameter,  with  a  hole  in 
the  centre  drilled  and  tapped  T5^  in.  to  fit  the  screwed 
shaft.  The  side  of  the  nut  which  is  to  go  next  to  the 
discs  should  be  faced  up  true  on  a  screw  mandrel,  and 
the  outside  corner  rounded  off  as  shown  in  the  drawing. 
Two  parallel  flats  are  filed  on  the  edge  (see  Fig.  135, 
p.  138)  to  take  a  spanner. 

Put  the  core  discs  on  the  shaft,  the  painted  sides  all 
facing  one  way;  see  that  the  core  is  in  the  right 
position  lengthways  on  the  shaft,  and  that  the  channel 
L,  Fig.  135,  for  the  insulated  wire  is  straight;  then 


132         DYNAMOS  AND  ELECTRIC  MOTORS. 

screw  up  the  nuts  as  tight  as  possible,  leaving  the  flats 
flush  with  the  channel ;  a  little  oil  between  the  face  of 
the  nut  and  end  disc  assists.  Test  the  shaft  between 


centres,  and,  if  required,  straighten  it ;  then  turn 
down  the  necks  to  fit  the  bearings.  When  a  good  fit  is 
attained,  place  the  armature  in  the  field  magnet  and  fix 
the  brackets  in  place.  The  armature  should  be  central 
in  the  bore  and  should  spin  freely  with  the  fingers ;  if 
stiff,  ease  the  shaft  bearings  until  it  runs  freely  and  yet 


UXDERTYPE  DYNAMO  AND  MOTOR.        133 

without  shake.  An  end  movement  of  about  -^  in.  is  ad- 
visable. The  armature  core  should  coincide  lengthways 
with  the  field  magnet ;  should  it  project  from  one  side 


more  than  the  other,  the  magnet  will  try  to  pull  it  into 
a  central  position.  In  doing  this  it  pulls  against  a  bear- 
ing, which  will  have  a  tendency  to  get  hot.  Any  of  the 
core  plates  that  project  can  be  levelled  down  with  a  file. 
The  commutator  consists  of  a  piece  of  brass  tube  M, 


134        DYXAUOS  AXD  ELECTRIC  MOTORS. 

Fig.  134,  fixed  on  a  wooden  bush  and  carried  on  the  arma- 
ture shaft.  The  brass  tube  is  divided  into  two  equal 
segments  by  saw-cuts  nearly  parallel  to  the  axis  of  the 
shaft,  one  portion  being  connected  to  one  end  of  the 
armature  wire  and  the  other  portion  to  the  other.  It  is 
essential  that  the  two  portions  must  not  be  in  metallic 
communication  except  through  the  armature  wire,  and 
the  segments  must  not  be  in  metallic  communication 
with  the  shaft.  The  commutator  may  be  a  piece  of  seam- 
less drawn  tube,  and  should  be  a  little  over  1  in.  outside 
diameter  and  f  in.  long.  The  thickness  may  be  about 
i  in.,  so  as  to  allow  for  truing  the  surface  from  time  to 
time  as  it  becomes  worn  by  the  brushes.  The  hardwood 
insulating  bush  o,  Fig.  134,  will  be  |  in.  long.  Through 
its  centre  drill  the  hole  for  the  armature  shaft,  using  the 
same  drill  as  for  the  bearings,  and  ream  it  out  to  fit 
tightly  on  the  shaft.  It  is  best  to  use  a  mandrel  to  turn 
the  bush  on,  and  when  this  has  been  done  the  tube  should 
be  fixed  with  cement  and  left  to  set.  The  bush  must  pro- 
ject I  in .  at  the  end  nearest  the  bearing.  Mark  off  centres 
for  two  holes  in  the  tube  at  diametrically  opposite  points 
for  the  screws  which  are  to  hold  the  commutator 
segments  to  the  bush.  These  holes  may  be  J  in.  diam. 
countersunk  into  the  tube,  so  that  the  screw-heads  will 
come  nearly  flush,  just  leaving  enough  projecting  to  quite 
fill  the  hole  up  when  the  outside  of  the  tube  has  been 
turned  true.  These  screws  should  be  of  brass,  and  must 
fit  tightly,  or  when  turning  up  the  commutator  they 
will  come  loose.  It  is  very  important  to  have  these 
screws  short,  so  as  not  to  touch  the  shaft,  as  there 
must  be  no  metallic  connection  between  the  tube  and 
the  shaft. 

Mark  on  the  tube  two  diametrically  opposite  lines 
running  from  one  end  to  the  other  midway  between  the 
ecrews  just  put  in.  These  lines  are  to  locate  the  posi- 
tions for  the  cuts  p,  Fig.  132  (p.  133),  which  separate  the 
tube  into  equal  parts.  These  cuts  are  sawn  about  -^  in. 
wide,  and  aslant,  as  shown  in  Fig.  128  (p.  125) ;  this 
causes  the  brushes  to  pass  from  one  segment  to  the  other 


UNDERTYPE  DYNAMO  AND  MOTOR.        135 

gradually,  and  lessens  the  sparking  and  wear.  The 
amount  of  slant  is  not  important ;  a  deviation  of  about 
iV  in.  each  side  of  the  centre  line  will  do.  Saw  down  to 
the  bush  and  slightly  into  it,  so  as  to  separate  the  seg- 
ments completely  ;  see  that  the  slot  is  perfectly  clear  of 
cuttings ;  and  to  keep  the  segments  apart  and  prevent 
dust  from  getting  into  the  slot,  insert  a  thin  strip  of 
wood  or  mica.  A  little  cement  or  shellac  varnish  will 
keep  it  in  place.  In  each  brass  segment,  at  the  end  next 
to  the  armature  core,  saw  a  nick  just  large  enough  to 
allow  the  ends  of  the  armature  wire  to  go  in  and  fit 
tightly.  The  complete  commutator  may  now  be  gently 
driven  on  the  shaft,  the  slots  being  in  line  with  the  round 
part  of  the  core,  as  shown  by  Fig.  137  (p.  142)— that  is,  at 
right  angles  to  the  centre  of  channel  L,  Fig.  135  (p.  138). 

The  oil-guard  K,  Fig.  133,  can  be  of  brass,  and  is 
driven  tight  on  the  shaft  after  the  commutator  is  in 
place.  The  oil-guards  for  the  pulley  ends  can  be  tapped 
to  fit  the  screwed  part  of  the  shaft,  or  made  to  fit  the 
plain  part,  and  can  be  put  in  place  after  the  armature 
is  wound. 

To  fit  up  the  brush  gear,  Figs.  131,  132,  and  133,  com- 
mence with  the  rocker  T,  Fig.  132  (p.  132).  This  allows 
the  brushes  to  be  moved  round  the  commutator  in  order 
to  find  the  position  which  gives  best  results  when  working. 
Bore  a  hole  about  £  in.  in  diameter  in  the  boss  u  to  fit 
on  to  the  boss  on  the  bracket,  so  that  the  arm  is  straight 
and  square  with  the  hole.  Put  the  rocker  on  a  mandrel 
and  face  each  side  of  the  boss.  Now  put  the  bearing 
bracket  on  a  mandrel,  and  turn  down  the  projecting 
boss  to  fit  the  hole  in  the  rocker.  The  small  boss  at 
the  side  of  the  rocker  is  to  take  a  set-screw,  as  shown 
in  Fig.  132 ;  this  screw  should  fit  in  the  thread.  A 
piece  of  hard  wood  is  required  for  the  crosspiece  to 
carry  the  brush-pins  (see  v,  Fig.  131).  This  should  be 
filed  up  about  \\  in.  by  £  in.  by  \  in.  thick ;  the  angle 
to  receive  it  must  be  filed  out  square  to  the  hole  in  boss, 
so  that  when  the  crosspiece  is  fixed  in,  the  pins  will 
come  parallel  to  the  shaft.  Mark  the  exact  centre  of 


136 


DYNAMOS  AND  ELECTRIC  MOTORS 


the  crosspiece,  and  drill  a  hole  to  clear  a  countersunk 
screw  \  in.  diameter.  Now  place  the  crosspiece  in  posi- 
tion in  the  angle  of  the  rocker  arm,  so  that  it  projects 
equally  at  each  side,  and  with  a  scriber  mark  off  on  the 


Fig.  133.— End  View  of  Dynamo. 

brass  the  position  of  the  hole  ;  drill  and  tap  it  to  fit  the 
screw.  The  crosspiece  can  now  be  fixed  in  place.  At 
|  in.  on  each  side  of  the  middle,  mark  centres  for  the 
brush-pins,  on  the  centre  line  of  the  crosspiece,  and  drill 
and  tap  two  holes  &  in  diameter. 

The  brush-holders  w,  Fig.  131  (p.  132),  must  be 
finished  next.  The  castings  should  be  filed  all  over,  and 
the  ends  squared.  Mark  the  centre  at  one  end  of  the 


UNDERTYPR  DYNAMO  AND  MOTOR.        137 

circular  part  of  the  casting,  and  drill  a  -&-in.  hole  through 
it.  The  slots  for  the  brushes  can  be  cut  from  one  end 
with  a  saw,  as  shown  dotted  in  Fig.  131.  They  should  be 
^  in.  long  fully  -^  in.  wide,  and  parallel  with  the  holes 
already  drilled.  Drill  and  tap  the  bosses  for  £-in.  diameter 
clamping  screws,  as  shown.  These  bosses  may  be 
turned  by  putting  a  small  mandrel  in  the  screw-holes 
before  they  are  tapped  and  holding  the  mandrel  in  a 
chuck.  To  make  the  pins,  if  straight  ^~in.  brass  rods 
are  chosen  to  fit  the  holes  in  the  brush-holders  they  will 
only  need  to  be  polished.  Screw  one  end  of  each  pin  for 
a  length  of  ^  in.,  and  at  the  other  end  drill  a  small 
hole  through  the  diameter.  In  this  hole  place  a  pin  tc, 
prevent  the  brush-holder  from  being  forced  off  by  the 
spring.  The  pins  can  now  be  screwed  tightly  in  place 
in  the  cross-arm.  Make  two  hexagonal  nuts  to  screw 
on  the  threaded  part  which  projects  through  the  cross- 
arm  ;  these  are  to  clamp  the  flexible  wires  x,  Fig.  132, 
which  carry  current  to  the  terminals.  For  adjusting 
the  tension  on  the  springs,  two  collars,  as  shown,  are 
required.  They  may  be  made  from  |-in.  brass  rods, 
drilled  to  fit  the  pins,  and  each  should  be  fitted  with 
a  set-screw  to  fix  it  in  the  required  position.  A  small 
hole  is  drilled  in  the  face  at  one  side  of  each  collar  to 
take  one  end  of  the  spring,  and  a  similar  hole  should 
be  drilled  at  the  end  in  each  brush-holder  to  take  the 
other  end  of  the  spring.  The  spiral  springs  are  made 
of  hard  brass  wire,  about  No.  24  S.W.G.  ;  one  is  coiled 
left-handed,  and  the  other  right-handed. 

The  terminal  blocks  Y,  Fig.  133,  are  filed  all  over 
and  polished,  and  holes  are  drilled  and  countersunk  to 
take  wood  screws,  which  hold  the  blocks  down  on  the 
terminal- board.  A  hole  is  drilled  and  tapped  in  each 
block  at  the  end  next  the  commutator  to  take  J-in. 
cheese-head  screws,  which  clamp  the  field-wires  and 
brush-wires  (see  Fig.  131).  Holes  are  drilled  through 
the  upright  blocks  to  receive  the  outer-circuit  wires 
which  are  held  by  set-screws  put  in  from  the  top. 

The  terminal-board  z,  Figs.  132  and  133,  can    be 


138        DYNAMOS  AND  ELECTRIC  MOTORS. 

made  from  a  piece  of  mahogany  about  \\  in.  by 
2  in.  by  f  in.  thick,  and  polished  or  varnished  according 
to  taste.  Holes  are  drilled  in  it  to  take  two  ^e-in. 
countersunk  screws,  which  fix  the  board  to  the  field 
magnet.  The  holes  in  the  magnet  should  be  drilled  and 


Fig.  134.— Armature  (Side  View). 


tapped  last,   and   marked   off  for  position  from   the 
terminal-board. 

The  driving  pulley  (shown  in  Figs.  132  and  133)  may 
be  made  suitable  for  either  a  flat  or  a  round  belt,  and  of 
dimensions  to  suit  the  manner  of  driving.  If  the 
dynamo  is  to  be  driven  from  a  foot  lathe  or  hand  wheel, 
a  pulley  about  1  in.  diameter  over  all  is  a  convenient 


Fig.  135.— Armature  (End  View). 

size,  with  a  V  groove  to  take  round  belt  of  ^  in. 
diameter.  The  width  of  the  pulley  should  be  about 
f  in.,  and  it  can  be  bored  with  a  tapering  hole  to  fit  a 
taper  shaft,  or  hole  and  shaft  can  be  made  parallel,  and 
a  set-screw  put  in  the  boss  will  hold  them  together.  The 
fit  should  be  good ;  and  when  the  armature  has  been  put 
between  centres  and  the  pulley  finally  turned  true  in 
its  place,  the  mechanical  construction  is  finished. 

To  proceed  with  the  insulation.    Take  the  armature 
out  and  the  bearings  off.    Examine  the  field  magnet 


UNDER  TYPE  DYNAMO  AND  MOTOR.        139 

where  the  wire  is  to  be  wound,  and  with  a  file  smooth 
off  all  corners,  any  rough  places,  and  all  sharp  edges  and 
points  likley  to  cut  through  the  insulation.  Wrap  two 
layers  of  thick  brown  paper  round  each  core,  sticking 
them  on  with  shellac  varnish.  Cut  out  four  rectangular 
cardboard  cheeks  or  flanges  Q,  Figs.  132  and  133,  to 
fit  the  cores  ;  the  wire  will  extend  about  f  in.  from  the 
core,  so  the  cheeks  must  be  made  to  suit ;  they  can  be 
sprung  on  the  cores  if  a  slanting  cut  is  made  across  one 
side  and  a  piece  of  paper  is  pasted  over  the  cut  to  keep 
it  together  when  the  cheeks  have  been  pushed  to  their 
places  at  the  ends  of  the  core.  Carefully  look  over 
the  insulation  and  see  that  it  is  sound  everywhere,  so 
that  the  wire  cannot  come  into  contact  with  the  iron 
at  any  point.  Then  brush  a  thick  coat  of  shellac  over  the 
paper  wrapping  and  cheeks,  and  leave  them  until  quite 
dry. 

The  armature  must  be  treated  in  a  similar  way. 
Smooth  all  projecting  points,  edges,  and  corners  along 
the  channel  where  the  wire  is  to  be  wound ;  then  with  a 
single  layer  of  thick  brown  paper  cover  the  channel,  the 
ends  of  the  core,  and  the  shaft  to  the  oil-guard  at  the 
pulley  end  and  to  the  commutator  at  the  other  end. 
Leave  the  paper  projecting  a  little  beyond  the  edges  of 
the  channel,  so  as  to  be  sure  that  the  insulation  comes  up 
to  the  edges  ;  it  can  be  trimmed  down  after  the  wire  is 
wound  on.  The  edges  at  the  ends  of  the  channel  can 
have  an  extra  thickness  of  paper  put  on  over  the  first 
covering,  as  the  covering  on  the  wire  is  liable  to  be 
cut  through  at  these  points.  Examine  the  insulation  ; 
if  all  right,  give  it  a  thick  coat  of  shellac  and  leave  to 
dry. 

To  wind  the  field-magnet  requires  about  2  Ibs.  of 
No.  22  S.W.G.  single  cotton-covered  copper  wire,  which 
may  be  wound,  layer  by  layer,  by  hand,  in  the  direction 
shown  in  Fig.  136,  keeping  it  as  even  as  possible  with 
a  moderate  tension.  The  number  of  layers  is  not 
important,  and  the  winding  may  be  finished  either 
at  the  top  or  bottom.  It  does  net  matter  greatly 


140        DYNAMOS  AND  ELECTRIC  MOTORS. 

if  the  number  of  layers  on  each  core  is  not  quite  the 
same ;  try  to  put  about  1  Ib.  of  wire  on  each  core ; 
but  it  is  essential  for  the  winding  to  be  in  the 
direction  shown  in  Fig.  136,  and  kept  so  throughout. 
As  each  layer  is  finished  it  should  be  brushed  all  over 
with  sufficient  shellac  varnish  to  give  the  surface  a 
good  coat.  The  commencing  ends  of  the  wire  B  and  A, 
Fig.  136,  which  reach  from  the  core  outwards,  should 
be  wrapped  round  with  thin  paper  along  the  part 
which  is  buried  in  the  end  of  the  coil,  and  varnished 
with  shellac  to  make  sure  that  the  current  goes  straight 
to  the  innermost  layer  and  does  not  leak  away  to  the 
other  layers.  The  current  must  go  through  the  wire 
from  end  to  end  without  making  a  short  cut  across  at 
any  point.  If  a  bare  or  frayed  place  is  found  while 
winding,  cover  it  with  some  thin  paper.  The  most 
convenient  way  to  wind  the  coils  is  to  fix  a  strip  of 
wood  to  the  top  of  the  magnet  by  the  terminal-board 
screws,  and  then  to  fasten  the  wood  to  a  face-plate 
fixed  on  the  lathe,  bringing  each  core  in  turn  to 
the  centre.  If  the  weight  of  the  overhanging  core  is 
counterbalanced,  the  magnet  will  be  rotated  more 
conveniently ;  turn  the  face-plate  round  with  the 
left  hand,  guiding  on  the  wire  with  the  right  hand, 
assisted  by  the  left  where  the  wire  requires  passing 
between  the  cores.  The  magnet  may  be  made  with  a 
joint  through  the  top  to  allow  of  winding  the  coils  in 
the  lathe,  if  the  joint  is  made  to  be  in  close  contact  all 
over  the  surface.  The  extra  trouble  taken  to  wind 
the  coils  as  described  is  nothing  compared  with  extra 
work  needful  to  construct  the  joint  and  magnet  in  one 
piece  in  the  way  mentioned.  Completely  wind  one  core 
first  to  the  full  depth  of  the  cheeks,  and  then  pro- 
ceed with  the  other,  joining  the  ends  to  make  the 
final  connections.  Cover  the  last  layer  with  two  or 
three  coats  of  shellac  varnish. 

To  wind  the  armature  requires  about  J  Ib.  of  No.  20 
S.W.G.  double  cotton- covered  copper  wire.  Put  the 
armature  in  the  lathe  between  centres,  with  the  com- 


UNDERTYPE  DYNAMO  AND  MOTOR.        141 

mutator  to  the  right  hand.  Commence  from  the  right- 
hand  end  and  lay  the  wire  from  there,  along  the  channel 
to  the  left-hand  end,  then  across  the  end  and  under- 
neath along  the  channel  to  the  right-hand  end,  across 
the  channel  for  one  layer,  then  back  again  for  second 
layer.  Get  on  as  much  wire  as  possible,  and  continue 
winding  until  the  channel  is  quite  full 


Fig.  136.— Field  Magnets,  showing  Method  of  Winding. 

Each  layer"  of  wire  should  have  a  coat  of  shellac 
varnish.  If  found  more  convenient,  the  portion  of  the 
channel  on  one  side  of  the  shaft  may  be  filled  up  first 
and  then  that  on  the  other  side.  Having  commenced  to 
wind  the  wire  round  the  core  in  a  certain  direction,  this 
direction  must  be  maintained  right  through,  as  is  shown 
by  Fig.  25  (p.  23).  It  is  easy  to  reverse  the  direction  of 
the  winding  when  passing  from  one  side  of  the  shaft  to 
the  other,  and  care  must  be  taken  to  avoid  this  mistake. 


142         DYXAMOS  AND  ELECTRIC  MOTORS. 

The  wire  being  all  wound,  bind  it  tightly  with 
strong  thin  cord  wrapped  round  the  centre  groove  of 
the  core  K,  Fig.  134,  prepared  to  receive  it.  This  makes 
an  even  binding  about  \  in.  long,  and  it  prevents  the 
wires  swaying  outwards  owing  to  centrifugal  force 
when  the  armature  is  rotating.  The  beginning  and 
the  finishing  ends  of  the  wire  on  the  armature  must 
now  be  connected  to  the  commutator.  One  end  goes 
to  each  segment,  and  both  must  be  soldered  into  the 
nicks  made  for  them  ;  it  is  well  also  to  bind  some  cord 
round  these  wires  to  keep  them  in  place.  When  all  is 
finished,  give  the  wire  and  binding  cord  a  thick  coat 
of  shellac. 

The  commutator  can  now  be  finally  trued  up  in  the 
lathe,  taking  a  very  light  cut,  to  remove  any  surplus  solder 


Fig.  137. — Position  of  Commutator  on  Armature. 

and  to  make  it  run  quite  true.  Put  a  disc  of  thin  card 
between  the  pulley-end  oil -guard  and  the  armature  wire, 
to  prevent  any  chance  of  damaging  the  insulation. 

The  dynamo  can  now  be  finally  put  together.  The 
field- wires  are  connected  up  to  the  terminal  blocks  as 
shown  in  Figs.  132,  133,  and  134,  and  also  joined  to- 
gether in  the  centre  as  shown  in  Fig.  136.  This  last  joint 
should  be  twisted  and  soldered  to  make  good  contact. 
Connect  the  brush-holder  pins  by  flexible  copper  wires  to 
the  terminal  blocks,  so  that  the  rocker  may  be  easily 
moved.  These  flexible  wires  are  made  by  coiling  some 
No.  20  S.W.G.  insulated  wire  on  a  rod  T\  in.  diameter, 
just  as  spiral  springs  are  made  ;  enough  of  the  wire  at 
each  end  is  stripped  of  its  covering  to  make  contact  with 
the  clamping  screws. 


UNDERTYPE  DYNAMO  AND  MOTOR.         143 

The  brushes  may  be  made  of  sheet  copper  or  of  copper 
wire  ;  they  should  be  flexible,  to  make  good  contact 
with  the  commutator  and  brush-holders.  A  good 
brush  may  be  made  from  copper  wire,  about  No.  24 
S.W.G.  ;  fix  one  end  in  a  vice,  take  hold  of  the  other  end 
with  a  pair  of  pliers  and  give  a  fair  pull,  to  stretch  the 
wire  a  little  and  straighten  it.  Cut  off  sufficient  pieces, 
each  2  in.  long,  to  make  two  brushes  each  J  in.  wide,  and 
at  one  end  solder  the  wires  together.  It  is  a  good  plan 
to  curve  the  brush  where  it  touches  the  commutator, 
so  that  there  is  a  surface  of  contact  about  J  in.  broad  all 
along  the  brush. 

The  dynamo  is  now  complete,  but,  to  commence 
with,  its  field  magnet  requires  exciting  ;  afterwards  it  will 
always  excite  itself.  The  direction  for  running  is  that  of 
the  hands  of  a  clock,  when  the  observer  looks  at  the  side 
of  the  pulley  as  if  looking  at  a  clock  face.  Rotate  the 
armature  in  this  direction  at  a  high  speed ;  if  it  sud- 
denly works  stiffly  and  sparks  appear  at  the  brushes,  it 
has  started  itself  all  right,  and  the  field  magnet  will  not 
require  any  further  assistance  ;  but  if  this  does  not 
occur,  and  the  dynamo  fails  to  light  a  10-volt  lamp,  an 
electric  battery  will  be  required  to  give  the  field  magnet 
the  necessary  start.  Put  a  piece  of  paper  between  one 
of  the  brushes  and  the  commutator  to  prevent  the 
current  going  through  the  armature.  Now,  looking  from 
the  commutator  end,  connect  the  positive  wire  of  a 
strong  battery  to  the  right-hand  terminal,  and  the  nega- 
tive wire  to  the  left-hand  terminal.  While  the  batteiy 
is  thus  connected,  gently  tap  the  iron  of  the  field  magnet 
with  a  hammer  for  half  a  minute  ;  disconnect  the  battery, 
remove  the  paper  from  under  the  brush,  and  on  driving 
the  armature  again  the  machine  should  work  all  right. 
The  output  of  this  dynamo,  with  3,000  revolutions  per 
minute,  is  about  10  volts  at  5  amperes  ;  but  it  will  give 
higher  electro-motive  forces  up  to  about  20  volts  with 
less  current  if  run  at  higher  speeds.  The  dynamo  can 
be  painted  to  suit  taste. 


144 


CHAPTER   XH. 

440- WATT  MANCHESTER  TYPE   DYNAMO. 

THE  dynamo  described  in  this  chapter  is  of  the  Man- 
chester type,  shunt  wound,  and  designed  for  an  output 
of  440  watts — viz.  8  amperes  at  55  volts — when  run- 
ning at  1,800  revolutions  per  minute.  Figs.  138  and 
139  (pp.  145  and  147)  show  a  plan  and  an  end  view  of 
the  machine  complete. 

The  field  magnet  castings  can  be  bought  with  the 
armature  tunnel  bored  out,  5^  in.  diameter,  and  the 
field  magnet  cores  fitted.  The  base  of  each  pedestal  is 
turned,  making  the  centring  of  the  armature  in  the 
tunnel  much  easier  than  when  a  flat-bottomed  pedestal 
is  used.  The  field  magnet  cores,  2f  in.  diameter  and 
5j  in.  long,  are  wound  with  11  Ib.  of  No.  20  S.W.G. 
cotton-covered  wire — 5^  Ib.  being  wound  on  each  core. 
The  direction  of  the  winding  is  shown  in  Fig.  141 
(p.  151),  producing  a  north  pole  at  the  top  and  a  south 
pole  at  the  bottom. 

The  field-magnet  bobbin  ends  may  be  fixed  by 
turning  a  shoulder  on  each  end  and  shrinking  on  these 
shoulders  circular  plates  of  iron  ^  in.  in  thickness. 
But  if  unable  to  turn  these  shoulders,  the  bobbin  end.s 
may  be  made  of  either  sheet  brass,  sheet  vulcanite  ^  in. 
thick,  or  thin  hard  wood.  To  make  wood  ends,  procure 
eight  sheets,  each  £  in.  thick,  by  6  in.  square,  of  any 
close-grained  hard  fretworking  wood,  such  as  pear, 
holly,  walnut.  Glue  pairs  of  the  sheets  together 
face  to  face,  with  the  grain  of  one  running  at  right 
angles  to  the  grain  of  the  other,  and  cramp  them 
in  a  flat  press  for  twenty-four  hours,  thus  making  four 
sheets  |  in.  thick.  Then  screw  the  four  sheets  together 
at  their  corners,  mount  them  on  the  face-plate  of  a 
lathe,  and  in  the  centre  bore  a  hole  to  fit  the  magnet 


MANCHESTER  TYPE  DYNAMO.  145 

cores  tightly.    Turn  the  outside  to  make  a  disc  5  in. 
diameter,  and  thus  make  the  bobbin  ends. 

The  cores  of  the  field  magnet  are  drilled  at  each  end, 
and  tapped  £  in.  A  stud  3  in.  long  is  screwed  into  one 
end,  and  in  the  other  end  place  a  hexagon-headed  bolt 
3  in.  long.  Centre  the  end  of  the  stud  and  the  bolt 
head,  and  place  the  core  between  the  lathe  centres  to 
see  that  it  runs  fairly  true.  Then  paint  the  core  with 
Brunswick  black,  and,  while  wet,  push  the  bobbin  ends 
on  and  paint  them  on  the  inside  and  round  the  joint. 
The  ends  of  the  cores  must  be  left  clean  and  bright, 


Fig.  138. — Plan  of  Manchester  Dynamo. 

otherwise  they  will  make  a  bad  joint  with  the  pole- 
pieces,  and  so  lower  the  efficiency  of  the  dynamo. 

Winding  the  wire  direct  on  the  core  would  tend  to 
force  off  the  bobbin  ends.  Pieces  of  wood  i  in.  thick 
and  5  in.  square,  with  holes  in  the  centre  to  pass  over 
both  the  stud  and  the  bolt,  and  pressed  against  the  ends 
of  the  cores  by  two  i-in.  nuts,  will  prevent  this.  The 
wire  can  be  wound  on  evenly  by  hand  in  the  lathe,  using 
a  very  slow  speed.  It  should  previously  be  coiled,  and 
placed  so  that  it  may  run  freely  ;  and  can  then  be  run 
through  the  hand  without  causing  kinks.  An  empty 


146         DYNAMOS  AND  ELECTRIC  MOTORS. 

bobbin  held  in  the  palm  of  the  hand,  for  the  wire  to 
run  over,  will  avoid  making  the  fingers  sore. 

A  coat  of  shellac  varnish  should  be  given  each  layer, 
and  allowed  to  dry  ;  then  wind  back,  and  so  continue 
until  all  the  wire  is  wound  on.  When  both  cores  are 
wound,  put  them  in  a  warm  place  for  a  few  hours  to 
dry  and  harden. 

The  armature  is  5  in.  diameter  and  4  in.  wide,  and 
is  built  up  of  150  soft  iron  cog-ring  stampings,  having 
ten  channels  1  in.  wide  and  £  in.  deep.  An  easy 
method  of  insulating  the  laminations  is  to  cut  150  sheets 
of  tissue  paper  6  in.  square,  and  with  shellac  varnish 
paste  a  sheet  on  each  stamping.  Then  thread  the 
stampings  together  with  five  brass  rods  J  in.  diameter 
and  5  in.  long,  screwed  each  end  for  f  in.  Put  washers 
on  the  brass  rods  to  equal  the  thickness  of  the  bosses  on 
the  spider  arms,  and  screw  up  the  end  nuts  until  the 
armature  is  4  in.  wide,  using  the  calipers  to  ascertain 
that  the  end  faces  are  parallel. 

Fig.  140  (p.  149)  shows  a  section  through  the  spiders. 
The  outside  is  comparatively  flat,  and  the  inside  has  a 
central  boss  and  also  smaller  bosses  near  the  end  of 
each  arm.  A  circle  4j  in.  diameter  ought  to  bisect  each 
boss  on  the  end  of  the  five  arms.  In  the  centre  of  each 
boss  drill  a  J-in.  hole  to  receive  the  ends  of  the  brass 
rods.  If  the  rods  do  not  enter  their  respective  holes,  the 
spider  arms  may  be  bent  by  light  blows  with  a  hammer. 

When  the  spiders  are  bolted  on  the  armature,  run  it 
between  the  lathe  centres,  and  adjust  centre  dots  placed 
in  the  spiders  till  the  whole  runs  true.  Having  marked 
the  position  of  the  spiders,  take  them  off  and  bore  a 
|-in.  hole  in  the  central  boss  of  each.  Decide  which 
one  is  going  to  be  placed  at  Jthe  commutator  end,  and 
in  it  file  a  keyway  J  in.  wide  and  T%  in.  deep ;  this 
should  be  under  one  of  the  arms,  so  as  to  weaken  the 
spider  least. 

The  steel  spindle  is  shown  at  Fig.  140  (p.  149) ;  it  ia 
14|  in.  long,  its  collar  being  Ij  in.  by  J  in.  The  central 
portion  is  \  in.  diameter  by  7|  in.  long,  the  journals  being 


MANCHESTER   TYPE  DYNAMO.  147 

Q  in.  diameter  by  2£  in.  long.  The  keyway  must  bo  cut 
at  the  commutator  end  £  in.  deep  and  J  in.  wide  for  a 
length  of  3£  in.  A  keyway  -^  in.  wide  and  deep  must 
also  be  cut  at  the  pulley  end. 

The  bearings  are  of  cast  iron,  and  their  bases  have 
the  same  radius  as  that  of  the  armature  tunnel,  the 
bearing  steps  being  turned  and  the  tunnel  bored  at  the 
same  operation.  The  web  of  the  bearing  stands  out- 
wards when  in  position.  Bore  each  bearing  to  take  the 
shaft,  and,  at  the  inner  side  of  the  bearing  at  the  com- 
mutator end,  turn  a  shoulder  Ij  in.  diameter  and  £  in. 


nrn 


rim. 


Fig.  139.— End  View  of  Dynamo. 

wude  to  take  the  brush  rocker.  In  the  top  of  each 
bearing  drill  and  tap  an  £-in.  gas-thread  hole  for  a 
lubricator.  Mount  the  bearings  together  on  a  mandrel, 
and  turn  up  their  bases.  They  are  fixed  with  |-in.  bolts. 
The  height  for  the  bearings  may  be  found  by  trying 
the  armature  when  it  is  mounted  on  the  shaft,  to  see 
that  the  air  space  is  equal  above  and  below. 

The  cast-iron  driving  pulley  is  2£  in.  diameter  by 
ij  in.  across  the  face.  It  should  be  bored  to  f  in., 
and  fastened  to  the  shaft  with  a  key  ^  in.  wide.  The 
depth  of  the  slot  in  the  pulley  should  be  J  in.  This 
key  must  have  a  head,  so  that  it  can  be  drawn  when 
required. 

File  or  turn  three  grooves  f  in.  wide  and  <fa  in.  deep 
round  the  armature  stampings,  to  take  binding  wire,  as 
explained  on  p.  54,  one  groove  in  the  centre  and  the 


148         DYNAMOS  AND  ELECTRIC  MOTORS. 

other  two  1  in.  from  each  end  of  the  armature. 
Sinking  the  binding  wire  into  the  iron  core  allows  a 
margin  for  wear  in  the  bearings,  and  gives  a  small  air 
space,  thus  tending  to  make  the  machine  more  efficient. 

Carefully  remove  all  sharp  corners  from  the  armature, 
as  if  the  stampings  cut  the  insulation  of  the  wire  the 
whole  coil  has  to  be  unwound,  the  insulation  repaired, 
and  finally  the  coil  rewound,  which  may  take  hours 
to  complete.  The  whole  of  the  armature  should 
now  have  a  coating  of  shellac  varnish.  When  an 
assistant  is  to  help  wind  the  armature,  the  shaft 
and  spiders  are  removed  ;  it  is  then  laid  on  a  trestle 
and  held  firmly  down  by  a  strip  of  wood  passed 
through  the  core.  For  a  single-handed  job,  fasten  it 
down  to  a  table,  as  shown  on  p.  68,  so  that  it  will  thus 
be  possible  to  work  at  it  sideways,  and  get  at  each  end. 

Before  winding  the  wire  the  channels  must  be  covered 
with  paraffin-soaked  tape,  one  layer  being  sufficient ;  as  a 
further  protection,  an  extra  strip  of  narrow  tape  may  be 
put  across  each  of  the  corners. 

The  wire,  consisting  of  5  Ib.  of  No.  17  S.W.G.  double- 
cotton-covered,  must  be  divided  into  ten  equal  lengths. 
To  do  this,  fix  two  empty  cotton-reels  at  a  distance  of 
45  ft.  apart ;  then  fasten  one  end  of  the  coil  to  one  reel, 
and  wind  the  wire  backwards  and  forwards  round  each 
reel  until  the  whole  coil  is  unwound.  The  wire  so 
wound  should  consist  of  ten  lengths,  but  if  there  is  any 
short  or  over,  measure  it  and  shift  the  reels  apart  so 
that  all  the  wire  is  used  in  ten  turns  round  the  two 
reels.  Then  cut  the  wires  where  they  pass  round  the 
reels,  and  produce  ten  equal  lengths.  By  placing  the 
reels  at  half  the  distance  apart  and  cutting  at  one  end 
only,  the  same  result  is  to  be  obtained.  Each  length 
must  be  loosely  coiled,  soaked  in  melted  paraffin  wax, 
and  allowed  to  drain  and  harden.  Proceed  to  wind  one 
of  these  coils  on  a  wooden  shuttle,  24  in.  long,  l£  in.  wide, 
and  \  in.  thick,  the  ends  being  hollowed  out  like  a 
butcher's  tray  (see  Fig.  58,  p.  62).  Cut  from  hard  wood 
ten  pieces,  $  in.  square  and  1|  in.  long,  with  a  J-in  hole 


MANCHESTER  TYPE  DYNAMO.  149 

drilled  f  in.  from  the  end  of  each  piece,  and  secure  them 
to  the  ends  of  the  brass  rods,  as  shown  at  A,  in  Fig.  141 
(p.  151),  to  take  the  place  of  the  spider  arms.  The  enda 
of  the  coils  are  kept  in  position  by  these,  and  the  wire 
is  prevented  from  getting  under  the  spider  arms  when 
they  are  being  placed  on  to  the  ends  of  the  armature. 

When  the  armature  is  in  position  for  winding, 
take  the  shuttle  of  wire,  cut  the  insulation  off  the  end 
for  a  distance  of  1  in.  or  so,  and  secure  it  to  the  bench 
by  a  screw.  Wind  the  wire  into  the  channel  by  bring- 
ing the  shuttle  over  the  armature,  and  passing  it  back 
through  it,  starting  at  the  left-hand  side  (when  looking 
at  the  commutator  end),  winding  to  the  right  and  then 


Fig.  140. — Longitudinal  Section  of  Dynamo. 

back  again  to  the  left,  and  so  on  till  all  the  wire  on  the 
shuttle  is  wound  on  the  armature,  finishing  at  the 
risht-hand  side.  Beat  the  wire  regular  by  a  small 
wooden  mallet,  or  by  a  piece  of  wood  struck  with  a 
hammer.  The  bulging  of  the  wire  on  the  inside  is  apt 
to  be  overlooked,  but  must  be  watched  for  carefully ; 
otherwise,  when  pushing  the  shaft  through  the  armature, 
it  may  damage  the  insulation.  A  galvanometer  should 
be  used,  if  possible,  for  testing  the  latter. 

When  this  coil  is  completely  wound,  3  in.  being  left 
to  connect  to  the  commutator  as  a  temporary  protec- 
tion to  the  wire,  wrap  a  band  of  calico  round  the  coil, 
securing  it  with  thread ;  then  proceed  to  wind  the  other 
coils  similarly.  The  commencing  end  of  one  coil  must 
be  soldered  to  the  finishing  end  of  the  next,  one  end  of 


150         DYNAMOS  AND  ELECTRIC  MOTORS. 

the  soldered  wires  being  made  into  an  eye,  and  secured 
to  a  commutator  strip  by  means  of  a  brass  headed 
screw.  Another  method  of  fastening  the  ends  of  the 
armature  coils  is  to  solder  both  the  wires  to  a  short 
length  of  brass  rod  screwed  vertically  into  the  end  of 
the  commutator  strip  (see  Fig.  54). 

When  all  the  coils  are  wound,  take  the  armature 
off  the  bench,  lay  it  on  one  end,  remove  the  five  pieces 
of  wood,  and  put  the  spider  on  quickly  and  carefully, 
all  corners  on  the  spiders  having  been  well  rounded. 
Next  turn  the  armature  the  other  end  up ;  place  the 
second  spider  on  the  shaft,  and  put  the  latter  through  the 
armature  and  through  the  first  spider ;  then  remove  the 
remaining  pieces  of  wood.  Put  the  spider  on  its  place, 
and  screw  up  the  nuts  until  both  the  spiders  ara  well 
home  ;  then  secure  the  nuts  with  soft  solder. 

The  commutator  and  the  spider  must  be  separated 
by  a  vulcanite  washer,  2j  in.  diameter  and  £  in.  or  ^  in. 
thick,  as  shown  in  Fig.  140  (p.  149).  The  binding-wire 
can  now  be  wound  round  the  armature  coils,  using 
No.  26  B.W.G.,  and  securing  each  band  with  solder  where 
it  crosses  the  iron.  Insulate  the  bands  from  the  arma- 
ture coils  by  strips  of  tape,  asbestos,  or  mica. 

The  casting  for  the  commutator  is  a  parallel  brass 
cylinder,  2  in.  outside  diameter,  1|  in.  wide,  and  J  in. 
thick.  This  has  to  be  mounted  on  a  cylindrical  block 
of  insulating  material,  and,  vulcanised  fibre,  ebonite,  or 
lignum-vitse  are  specially  suitable.  Boxwood  is,  however, 
more  likely  to  be  used.  Turn  a  piece  2;  in.  long,  and  of 
a  diameter  that  will  allow  it  to  be  driven  into  the  com- 
mutator casting ;  take  care  to  have  the  grain  running 
across  the  piece  diameter  ways,  or  it  will  split  when 
pushing  the  commutator  on  the  shaft.  Cut  from  one 
end  a  length  f  in.  (see  A  B,  in  Fig.  140),  while  the  wood 
is  in  the  lathe,  with  the  two  parted  surfaces  quite  flat. 
Divide  the  commutator  casting  round  the  outside  face 
into  twenty  equal  divisions  by  lines  parallel  to  tLe  axis. 
Ten  of  these  lines  taken  alternately  will  show  where  the 
saw-cuts  may  be,  the  other  ten  where  the  holding-down 


MANCHESTER  TYPE  DYNAMO.  151 

screws  must  be  placed.  In  each  strip,  on  the  latter 
line,  three  holes  must  be  drilled,  that  on  the  extreme 
left,  being  T\  in.  tapping  ;  the  next  ^  in.  away,  and  the 
third,  on  the  extreme  right,  being  both  countersunk  for 
a  Hn.  brass  screw.  When  all  the  holes  are  drilled  and 
tapped,  file  away  all  burrs  and  lumps  from  the  inside  of 
the  casting,  observing  that  the  button-headed  screws, 
which  are  fitted  to  the  TVin.  tapped  holes,  do  not  project 
inside  the  cylinder  when  screwed  down  to  the  head. 

Warm  the  casting  while  melting  some  glue,  which 
should  be  thin,  so  as  to  have  a  close  joint.  Then  drive 
in  the  short  piece  of  boxwood,  parted  face  first,  until 
flush  with  the  end  of  the  brass  cylinder ;  put  a  little 


Fig.  lil.— End  View  showing:  Method  of  Winding 
Armature  and  Fields. 


glue  on  the  parted  face  of  the  other  piece,  and  drive  it 
into  the  open  end  with  a  mallet,  so  that  the  grain  of  the 
two  pieces  is  at  right  angles  when  they  meet  in  the  centre 
of  the  brass  casting.  Directly  the  wood  is  driven  home 
place  the  whole  endways  between  the  jaws  of  the  vice, 
and  keep  it  under  pressure  for  some  hours.  If  the 
grain  were  uniform  across  the  cylinder,  some  screws 
fastening  the  commutator  strips  would  be  apt  to  strip  ; 
but  with  the  grain  at  right  angles  one  screw  is  sure  to 
hold. 

When  the  glued  joint  is  set  quite  hard,  screw  all  the 
brass  holding-down  screws  into  their  respective  holes; 
then  with  a  hack  saw  cut  through  the  casting  along  the 


152         DYNAMOS  AND  ELECTRIC  MOTORS. 

lines  already  drawn,  taking  care  not  to  saw  deeper 
than  -fa  in.  into  the  boxwood. 

When  all  the  strips  are  sawn  apart,  lift  each  alternate 
one,  singly,  and  clean  away  all  brass  filings,  etc. ;  then 
put  strips  of  mica  in  the  saw  cuts,  and  jam  them  tight, 
by  screwing  the  commutator  strip  home,  but  be  careful 
not  to  put  too  great  a  strain  on  the  brass  screws. 

The  boxwood  projects  at  the  end  carrying  the  button- 
headed  screws,  so  that  the  commutator  may  be  held 
in  a  chuck  when  boring  the  central  hole.  Bore  this 
hole  |  in.,  taking  care  not  to  get  it  too  large,  and  work- 
ing by  calipers,  as  it  is  impossible  to  try  it  in  place. 
Hand  pressure  is  sufficient  to  force  the  commutator  into 


Pig.  142.— Brash  Gear. 

place.  The  commutator  must  be  driven  by  a  vulcanite 
or  ebonite  key,  fitted  into  the  existing  keyway  in  the 
shaft,  but  which  need  go  no  more  than  \  in.  into  the 
boxwood.  When  the  commutator  is  mounted  on  the 
shaft,  turn  it  up  in  the  lathe,  using  a  fine-pointed  tool, 
and  taking  a  very  light  cut ;  then  finish  up  with  fine 
glass-paper,  not  emery-cloth. 

The  brush  rocker  and  brush  gear  are  shown  at 
Fig.  139  (p.  147),  with  the  rocker  fitted  to  the  bearing, 
together  with  one  brush  and  brush-holder.  The  brass 
rods  to  carry  the  holders  are  \  in.  in  diameter  by  l£  in. 
long,  turned  down  to  f  in.  for  another  \\  in.,  and 
screwed  for  £  in.  at  the  small  end.  Fig.  140  (p.  149) 
shows  a  half  section  of  the  brush  rocker,  with  a  vulcan- 
ised fibre  bush  and  washers  at  each  end. 

Fig.  142A  is  a  section  showing  an  easy  method  of 


MANCHESTER   TYPE  DYNAMO.  153 

regulating  the  pressure  of  the  brushes  upon  the  com- 
mutator by  means  of  the  piece  of  thin  spring  steel. 
The  width  at  the  lower  end  of  this  piece  of  steel  in 
exactly  that  of  the  space  between  the  cheeks  of  the 
brush-holder,  therefore,  when  the  strip  of  steel  is  secured 
to  the  ^brass  supporting  rod  by  the  small  steel  screw, 
there  is  no  side-play  in  the  brush-holder.  The  other 
end  of  the  steel  strip  is  J  in.  wide  and  3|  in.  long,  with 
a  nut  soldered  to  it,  and  has  a  ^  in.  thumb-screw.  The 
spring,  shown  in  plan  at  B,  is  about  4j  in.  long,  over  all. 

The  brushes  are  held  off  the  commutator  by  means 
of  the  steel  tongue  shown  in  position  at  A,  and  also  in 
detail  at  c. 

The  end  of  this  tongue,  which  is  bent  round  at  right 
angles,  must  be  secured  to  the  holder  by  a  TVin.  screw, 
the  other  end  having  a  Q  -shaped  hole,  so  that  when  the 
brush  is  off  the  commutator  this  hole  drops  over  the 
head  of  the  cheese-head  screw,  which  must  have  half  its 
head  partly  filed  down  to  receive  it.  To  release  the 
brush  the  tongue  must  be  lifted  with  the  finger  off  the 
screw-head.  The  larger  steel  spring,  through  which 
this  tongue  passes,  then  presses  the  brush  on  the  com- 
mutator with  a  pressure  that  can  be  adjusted  by  means 
of  the  thumb-screw  at  the  end  of  the  spring.  A  piece 
of  sheet  steel  as  wide  as  the  brush  is  fixed  so  that  the 
thumb-screw  presses  against  it,  and  a  similar  piece  is 
placed  on  the  top  of  the  brush,  extending  from  the 
brush-holder  to  the  toe  of  the  brush. 

When  the  machine  is  ready  for  trial,  secure  it 
to  the  floor,  and  connect  it  by  a  If-in.  belt  to  the 
driving-power.  Looking  at  the  commutator  end  of  the 
armature,  it  must  run  clockwise,  with  the  brushes 
diametrically  opposite,  and  pointing  in  the  direction  of 
rotation.  Connect  the  end  of  the  last  coil  of  the  left- 
hand  field  magnet  to  the  left-hand  brush,  and  the  last  or 
outside  coil  end  of  the  right-hand  field  magnet  to  the 
right-hand  brush,  the  two  ends  of  the  bottom  layers  of 
each  field-magnet  coil  being  joined  together.  Next 
connect  the  positive  pole  of  a  set  of  four  Leclanchtf  or 


154         DYNAMOS  AND  ELECTRIC  MOTORS. 

three  bichromate  cells  to  the  left  hand  brush,  and  the 
negative  pole  to  the  right-hand  brush.  One  of  these 
wires  must  be  cut  with  clean  ends,  so  that  they  can, 
when  brought  in  contact,  complete  the  circuit. 

Hold  the  two  ends  of  this  wire  in  the  hand,  and 
run  the  machine  at  about  1,800  revolutions  per  minute  ; 
then,  when  fully  under  way,  touch  the  two  ends  of  the 
wires  together.  If  the  batteries  are  in  good  condition, 
they  ought  to  be  strong  enough  to  start  the  magnetism 
in  the  field  magnets.  If  the  dynamo  begins  to  excite, 
the  first  thing  that  will  be  noticed  is  that  the  tone 
given  out  by  the  revolving  armature  will  change  from  a 
whirr  to  a  low  humming  sound  ;  sparks  also  will  be 
observed  at  the  brushes.  Directly  the  machine  starts  to 
excite,  disconnect  the  battery  circuit,  and  keep  the 
machine  running  for  a  few  minutes.  Then  stop  and 
connect  a  50-volt  16-candle-power  or  8-candle-power 
lamp  to  the  brush-holders  by  two  wires  of  any  con- 
venient length.  Run  the  machine  again,  and  the  lamp 
ought  to  light  up  when  running  at  1,800  revolutions  per 
minute.  If  the  machine  will  not  excite  the  first  time, 
cross  the  leads  from  the  field  magnets  to  the  brushes,  so 
that  the  right-hand  brush  is  connected  with  the  left- 
hand  coil  and  the  left-hand  brush  with  the  right-hand 
coil ;  then  run  the  machine  again,  and  if  unsuccessful, 
try  six,  then  eight,  batteries  in  series  to  excite  the 
field  magnets;  if  still  unsuccessful,  there  is  a  broken 
wire,  or  the  insulation  has  given  way  in  the  armature. 
This  must  be  discovered  and  repaired.  Then  connect  up 
six  more  lamps  of  16  candle-power  each,  one  by  one  as 
the  machine  is  running,  and  if  the  brushes  start  spark- 
ing, bring  them  slowly  forward,  by  means  of  the  rocker, 
in  the  direction  of  rotation  until  the  sparking  ceases. 
The  power  required  to  drive  the  machine,  when  under 
full  load,  will  be  about  £  brake  horse-power. 

Not  until  the  machine  works  properly  should  the 
finishing  touches  be  put  on. 


INDEX. 


Ailments  of  Small  Dynamos,  89 
Ampere,  Meaning  of,  13 

hour,  Meaning  of,  14 

Armature,  Meaning  of,  14,  76 

,  Cogged  King  or  Pacinotti,  17 

, ,  Winding,  146 

,  Double  Shuttle  or  Walker,  17 

,  Drum,  76 

for  50-watt  Undertype  Dynamo, 

130 
,  Fixing  to  Bench  for  Winding, 

• 

,  Gramme,  Building  up,  44 

,  Preparing  for  Winding. 

47 

,  Insulating,  67 

,  Manchester,  63,  146 

, ,  Winding,  148 

,  Method  of  Winding,  84,  148 

for  Model  Electro-motor,  100, 

lOt,  110 

of  Motor,  Preparing,  121 

,  Winding,  125 

,  King,  76 

,  Shuttle,  17, 18,  77 

.Siemens  H-girder,  21,  25 

, ,  Testing,  27 

, ,  Winding,  33 

of  Simplex  Dynamo,  66 

,  Speed  of,  83 

Armatures,  Classes  ot,  15,  76 


Armatures,  Laminated,  18,  25 

,  Ring,  When  Used,  77 

Attraction  and  Repulsion  of  PoK.-s, 

114 

B 

Batteries  for  Night  Lights,  etc.,  10 

,  Primary,  for  Lighting,  9 

Battery  for  Driving  Model  Motor, 
111 

for  Localising  Faults  in  Dy- 
namos, 89 

Bearings  of  Simplex  Armature,  72 

of  Manchester  Dynamo,  147 

Bed-plate  of  Simplex  Dynamo,  71 

of  Undertype  Dynamc,  91 

Belt  of  Simplex  Dynamo,  74 
Binding  Posts,  IS 

Screws,  18, 110 

Wires,  Use  of,  70 

Bobbin  Ends  of  Field  Magnets,  144 
Broken  Wires,  Joining,  20 
Brushes,    50-watt    Uudertype   Dy- 
namo, 135,  143 

of  Manchester  Dynamos,  153 

of  Model  Electro-motor,  102 

,  Position  of,  94 

of  Shuttle  Armature  Motor, 

128 

of  Siemens  Dynamo,  29,  31 

of  Simplex  Dynamo,  73 

.Sparking  at  the,  95 

Brush-holder  of  Gramme  Dynamo, 


'56 


DYNAMOS  AND   ELECTRIC  MOTORS. 


Brush-holder  of  Motor,  124 

of  Siemens  Dynamo,  30 

of  Simplex  Dynamo,  73 


Calculating     Wire      required     for 

Armature,  51 
Care  of  Dynam  js,  97 
Castings,  Cost  of,  22 

of  Gramme  Dynamo,  42 

,  Rough,  Trueing-up,  22 

for  Shuttle-Armature  Motor, 

120 

Clamp  for  Armature  Core,  68 

for  Holding  Brushes,  56 

Classification  of  Dynamos,  9 
Commutator   of   Crypto    Dynamo, 
134 

,  Firing  to  Shaft,  31 

—  of  Gramme  Dynamo,  49 
of  Manchester  Dynamo,  150 

of  Model  Electro  Motor,  102, 

124 

of  Siemens  Dynamo,  27 

of  Simplex  Dynamo,  70 

Compass,  Substitute  for,  89 

Compound  Winding,  40,  65 

Connecting  Wires  of  Dynamos,  39, 
153 

Connections,  Accidental,  93 

Connectors,  18 

Contact  Breaker,  110 

Spring,  109 

Cost  of  Dynamo  Castings,  22 

Current  from  Dynamo,  How  Calcu- 
lated, 80 

,  How  Determined,  76, 

79 

Currents,  Directions  of  in  Bar 
Magnets,  113 


Discs,  Preparing,  131 

Driving  Pulley  of  Crypto  Dynamo, 

138 
Dummy  Armature  and  Shaft,  Use 

of,  130 
Dynamo    for   Charging  Accumula 

tors,  90 

,  Definition  of,  10 

for  Electro-depositing,  90 

,  50-watt  Undertype,  129 

—  Gramme,  41 

,  Invention  of,  9 

for    Lighting    Pour    10-c.-p 

Lamps,  75 

to  Light  Two  8-c.-p.  Lamps,  66 

,  Manchester,  144 

,  Model,  Type  of  Armature  ton 

77 

,  Siemens,  21  • 

,  Simplex,  66 

Dynamos,  Classification  of,  9 


Electric  Current,   Explanation  of 

10 
Electrical  Energy,  Effects  of,  11 

Measurements,  13 

Electro  Motor  (See  Motor) 
Engine  to  Develop  i  Horse-power 

66 
Experimenting  with  Motors,  118 


Faults  in  Dynamos,  Localising,  89 

in  Winding,  31 

Field  Magnets.  Castings  of.  1?,0, 130, 
141 


INDRX. 


'57 


Field  Magnets,  Compound- Wound, 

65 
of    50-watt    Undertype 

Dynamo,  139 
of  Gramme  Dynamo,  12, 

44,57 

,  Length  of  Cores  of,  82 

,  of  Manchester  Dynamo, 

12,63 

of  Model  Motors,  98 

,  Overtype,  11 

of  Siemens  Dynamo,  22 

of  Simplex  Dynamo,  12,  71 

,  Types  of,  11 

,  Winding,  35,  57,  126,  139, 

144,  145 

" ,  Undertype,  11,  139 

Fifty-Watt  Undertype  Dynamo  and 

Motor,  129 

Finishing  Simpler  Dynamo,  74 
Former  for  Winding  Armature  of 

Simplex  Dynamo,  66 


Galvanometer,  Cost  of,  34 

,  Use  of,  34,  93,  149 

Gramme  Dynamo,  41 

,   Dimensions  and  Output 

of,  59 

,  Horse-power  to  Drive,  CO 

Guard  over  Armature  Gap,  91 


Handle  for  Moving  Rocker,  56 
Heating,  Excessive,  95 
Horse-power  to  Drive  Gramme  Dy 


Insulating  Armature,  67 

Brushes  of  Simple*    Dyt 

73 


nsulating  Commutator  Segments, 
27,50 

—  Varnishes,  83 
usulation,  Defective,  93 


oining  Wires,  67 


laminated  Armatures,  18,  25 
Laws  Governing  Electro-motors.  IIS 
Lead  of  Brushes,  32,  83 

.kage,  Discovering,  92 
in  Dynamos,  91 

ghting,  Electric  (See  Batteries  and 

Dynamos) 
Lubricator  for  Gramme  Dynamo,  47 


Magnetism  Neutralised,  91 

,  Want  of,  90 

Magnets,  Poles  of,  10,  37,  112 
Manchester  Dynamo,  61,  144 
Dimensions  and  Outputs 

of,  64 

,  Winding,  35 

Measurements,  Electrical,  13 

to  Drive  Small  Lathe,  119 

Driven  with  Two  Batteries,  118 

Motor,  50-watt  Undertype,  129 
Model,  made  without  Castings, 

H 

— ,  Shuttle  Armature,  119 
,  Small,  with  Horseshoe  Magnet 

and  Wooden  Saddle,  107 
Mounting  Motor,  128 


Ohm,  Meaning  of,  14 
Oil  Guards  for  50-watt  Undertypy 
Dynamo,  135 


158 


DYNAMOS   AND   ELECTRIC  MOTORS. 


Kacinotti,  41 

Armature,  17 

Piiii,  9 

Plug,    Wooden,    for    Armature    of 

Simplex  Dynamo,  70 
Polarity,  38 

,  Detecting  Alteration  of,  91 

Poles  of  Magnets,  10,  37,  112 
Primary  Batteries  for  Lighting,  9 


Repairing  Faults  in  Dynamos,  Tools 

for,  89 

Faulty  Wire,  93 

Rocker  for  Gramme  Dynamo,  55 

for  Manchester  Dynamo,  152 

Rotation  of  a  Motor,  Direction  of, 

112 
Running   50-watt    Undcrtype    Dy- 

namo,  143 

Hot,  95 

Manchester  Dynamo,  151 


Safe  Carrying  Capacity  of  Wire,  79 
Screws,  Faulty,  Replacing,  93 
Series  Connections,  39 

Motors,  Direction  of  Current 

in,  114 

and  Shunt   Dynamos,  Differ- 
ences between,  80,  83 

Shocks  from  Dynamos,  96 
Short  Circuiting,  40,  91 
Shuut  Connections,  40 

Motors,  Direction  of  Current 

in  117 

—  Wound  Dynamos,  Rules  for, 
81 


Shuttle- Armature  Motor,  119 

or  H-girder  Armature,  17 

for  Winding  Armatures,  52 

Siemens  Dynamo,  21 

Dynamos,    Table     of     Sizes, 

Wires,  Outputs,  etc.,  24 
Simplex  Dynamo,  66 
Dynamo  running  as   a  Motor, 

75 
Starting  Simpler  Dynamo,  74 


Taping,  36,  84 

Terminals  of  Dynamos,  19,  30,  74 

Testing  for  Insulation,  34,  149 

Shaft,  132 

Tools  for  Repairing  Dynamos,  89 


Varnish  for  Dynamos,  36,  46,  53,  14 >' 

Volt,  Meaning  of,  13 

Voltage,  How  Determined,  76,  78 

Obtainable  from  Small  Dyua 

mos,  77,  83 


Watt,  Meaning  of,  14 
Watts,  How  Determined,  80 
Winding  Armatures  of  Motors,  101, 

125 

Field  Magnet,  139 

50-watt  Undertype  Armature, 

140 

,  Detecting  Faults  in,  34 

Dynamo  Armatures,  33,  31,  51. 

52,  66,  84,  140,  148 

Field  Magnets  of  Motors,  126 

,  General  Hints  on,  33 

Gramma  Armature,  51,  52 


INDEX. 


159 


Win-ling  Gramme  Field  Maguets, 

57 

Manchester  Armature,  148 

Field  Magnets,  144, 145 

Siemens  Armature,  33 

Simple*  Armature,  66 

Of  Sories  Motors,  115 

Wire,  Armature,  Broken,  95 

for  Armature,  Calculating,  51 

,  Cheap,  Disadvantages  of,  81 

,  Circumferential  Velocity  of, 

78 
.  Copper,  Properties  of.  78 


Wire,  Dead  and  Active,  77 

,  Joining,  67 

for  Laminated  Cog-ring  Arma- 
ture, Calculating  Length  of,  87 

,  Preparing,  for  Winding,  35,84, 

148 

,  Protecting,  83 

,  Safe  Carrying  Capacity  of,  79 

for  Shuttle  Armature,  Calcu- 
lating Length  of,  85 

for    Small    Dynamos,    Calcu- 
lating, 76 

Wooden  Slab  for  Dynamo,  38 


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